Multi-layered cores having foam inner core for golf balls

ABSTRACT

Multi-layered golf ball core sub-assemblies and the resulting golf balls are provided. The core structure includes an inner core (center) comprising a foam composition, preferably foamed polyurethane. The intermediate core layer is preferably formed from a thermoplastic composition such as an ethylene acid copolymer ionomer resin; and the outer core layer is preferably formed from a thermoset composition such as polybutadiene rubber. The core layers have different hardness and specific gravity levels. In one preferred embodiment, the inner core has a positive hardness gradient, the intermediate core has a positive hardness gradient, and the outer core has a zero or negative hardness gradient. The core structure and resulting ball have relatively good resiliency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-assigned, U.S. patent applicationSer. No. 13/789,749 filed Mar. 8, 2013, now issued as U.S. Pat. No.9,050,501 with an issue date of Jun. 9, 2015, the entire disclosure ofwhich is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to multi-piece, golf ballshaving a solid core comprising layers made of foam, thermoplastic, andthermoset compositions. Particularly, the multi-layered core has a foaminner core (center), thermoplastic intermediate core layer, andsurrounding thermoset outer core layer. The core layers have differenthardness gradients and specific gravity values. The ball furtherincludes a cover of at least one layer.

2. Brief Review of the Related Art

Professional and recreational golfers normally play with multi-piece,solid golf balls. Such balls typically include an inner core made of anatural or synthetic rubber such as polybutadiene, styrene butadiene, orpolyisoprene. The ball further includes a cover surrounding the innercore. The cover protects the inner core and makes the ball more durable.The outer cover may be made from a variety of materials includingethylene acid copolymer ionomers, polyamides, polyesters, polyurethanes,and polyureas. The ball may further include one or more intermediatelayers disposed between the inner core and outer cover to impart otherproperties to the ball.

Manufacturers of golf balls use different materials to impart specificfeatures to the ball. For example, the resiliency and reboundingperformance of the golf ball are important properties and basedprimarily on the composition and construction of the core. The core actsas an engine or spring for the ball. In general, the reboundingperformance of the ball is determined by calculating its initialvelocity after being struck by the face of the golf club and itsoutgoing velocity after making impact with a hard surface. Moreparticularly, the “Coefficient of Restitution” or “COR” of a golf ballrefers to the ratio of a ball's rebound velocity to its initial incomingvelocity when the ball is fired out of an air cannon into a rigidvertical plate. The COR for a golf ball is written as a decimal valuebetween zero and one. A golf ball may have different COR values atdifferent initial velocities. The United States Golf Association (USGA)sets limits on the initial velocity of the ball so one objective of golfball manufacturers is to maximize COR under such conditions. Balls witha higher rebound velocity have a higher COR value. Such golf ballsrebound faster, retain more total energy when struck with a club, andhave longer flight distance.

The durability, spin rate, and feel of the ball also are importantproperties. In general, the durability of the ball refers to theimpact-resistance of the ball. Balls having low durability appear wornand damaged even when such balls are used only for brief time periods.In some instances, the cover may be cracked or torn. The spin raterefers to the ball's rate of rotation after it is hit by a club. Ballshaving a relatively high spin rate are advantageous for short distanceshots made with irons and wedges. Professional and highly skilledamateur golfers can place a back spin more easily on such balls. Thishelps a player better control the ball and improves shot accuracy andplacement. By placing the right amount of spin on the ball, the playercan get the ball to stop precisely on the green or place a fade on theball during approach shots. On the other hand, recreational players whocannot intentionally control the spin of the ball when hitting it with aclub are less likely to use high spin balls. For such players, the ballcan spin sideways more easily and drift far-off the course, especiallyif it is hooked or sliced. Meanwhile, the “feel” of the ball generallyrefers to the sensation that a player experiences when striking the ballwith the club and it is a difficult property to quantify. Most playersprefer balls having a soft feel, because the player experience a morenatural and comfortable sensation when their club face makes contactwith these balls. Balls having a softer feel are particularly desirablewhen making short shots around the green, because the player senses morewith such balls. The feel of the ball primarily depends upon thehardness and compression of the ball.

Manufacturers of golf balls are constantly looking to new materials forimproving the playing performance properties of the ball. For example,Puckett and Cadorniga, U.S. Pat. Nos. 4,836,552 and 4,839,116 discloseone-piece, short distance golf balls made of a foam compositioncomprising a thermoplastic polymer (ethylene acid copolymer ionomer suchas Surlyn®) and filler material (microscopic glass bubbles). The densityof the composition increases from the center to the surface of the ball.Thus, the ball has relatively dense outer skin and a cellular innercore. According to the '552 and '116 patents, by providing a shortdistance golf ball, which will play approximately 50% of the distance ofa conventional golf ball, the land requirements for a golf course can bereduced 67% to 50%.

Gentiluomo, U.S. Pat. No. 5,104,126 discloses a three-piece golf ball(FIG. 2) containing a high density center (3) made of steel, surroundedby an outer core (4) of low density resilient syntactic foamcomposition, and encapsulated by an ethylene acid copolymer ionomer(Surlyn®) cover (5). The '126 patent defines the syntactic foam as beinga low density composition consisting of granulated cork or hollowspheres of either phenolic, epoxy, ceramic or glass, dispersed within aresilient elastomer.

Aoyama, U.S. Pat. Nos. 5,688,192 and 5,823,889 disclose a golf ballcontaining a core, wherein the core comprising an inner and outerportion, and a cover made of a material such as balata rubber orethylene acid copolymer ionomer. The core is made by foaming, injectinga compressible material, gasses, blowing agents, or gas-containingmicrospheres into polybutadiene or other core material. According to the'889 patent, polyurethane compositions may be used. The compressiblematerial, for example, gas-containing compressible cells may bedispersed in a limited part of the core so that the portion containingthe compressible material has a specific gravity of greater than 1.00.Alternatively, the compressible material may be dispersed throughout theentire core. In one embodiment, the core comprises an inner and outerportion. In another embodiment, the core comprises inner and outerlayers.

Sullivan and Binette, U.S. Pat. No. 5,833,553 discloses a golf ballhaving core with a coefficient of restitution of at least 0.650 and acover with a thickness of at least 3.6 mm (0.142 inches) and a Shore Dhardness of at least 60. According to the '553 patent, the combinationof a soft core with a thick, hard cover results in a ball having betterdistance. The '553 patent discloses that the core may be formed from auniform composition or may be a dual or multi-layer core, and it may befoamed or unfoamed. Polybutadiene rubber, natural rubber, metallocenecatalyzed polyolefins, and polyurethanes are described as being suitablematerials for making the core.

Sullivan and Ladd, U.S. Pat. No. 6,688,991 discloses a golf ballcontaining a low specific gravity core and an optional intermediatelayer. This sub-assembly is encased within a high specific gravity coverwith Shore D hardness in the range of about 40 to about 80. The core ispreferably made from a highly neutralized thermoplastic polymer such asethylene acid copolymer which has been foamed. The cover preferably hashigh specific gravity fillers dispersed therein.

Nesbitt, U.S. Pat. No. 6,767,294 discloses a golf ball comprising: i) apressurized foamed inner center formed from a thermoset material, athermoplastic material, or combinations thereof, a blowing agent and across-linking agent and, ii) an outer core layer formed from a secondthermoset material, a thermoplastic material, or combinations thereof.Additionally, a barrier resin or film can be applied over the outer corelayer to reduce the diffusion of the internal gas and pressure from thenucleus (center and outer core layer). Preferred polymers for thebarrier layer have low permeability such as Saran® film (poly(vinylidene chloride), Barex® resin (acyrlonitrile-co-methyl acrylate),poly (vinyl alcohol), and PET film (polyethylene terephthalate). The'294 patent does not disclose core layers having different hardnessgradients.

Sullivan, Ladd, and Hebert, U.S. Pat. No. 7,708,654 discloses a golfball having a foamed intermediate layer. Referring to FIG. 1 in the '654patent, the golf ball includes a core (12), an intermediate layer (14)made of a highly neutralized polymer having a reduced specific gravity(less than 0.95), and a cover (16). According to the '654 patent, theintermediate layer can be an outer core, a mantle layer, or an innercover. The reduction in specific gravity of the intermediate layer iscaused by foaming the composition of the layer and this reduction can beas high as 30%. The '654 patent discloses that other foamed compositionssuch as foamed polyurethanes and polyureas may be used to form theintermediate layer.

Tutmark, U.S. Pat. No. 8,272,971 is directed to golf balls containing anelement that reduces the distance of the ball's flight path. In oneembodiment, the ball includes a core and cover. A cavity is formedbetween core and cover and this may be filled by a foamed polyurethane“middle layer” in order to dampen the ball's flight properties. The foamof the middle layer is relatively light in weight; and the core isrelatively heavy and dense. According to the '971 patent, when a golferstrikes the ball with a club, the foam in the middle layer actuates andcompresses, thereby absorbing much of the impact from the impact of theball.

One disadvantage with golf balls having a foam core is the ball tends tohave low resiliency. That is, the velocity of the ball tends to be lowafter being hit by a club and the ball generally travels shortdistances. Golf balls having foam inner cores are often referred to as“reduced distance” balls. There is a need for new balls having a foamcore with improved resiliency that will allow players to generate higherinitial ball speed. This will allow players to make longer distanceshots. The present invention provides new foam core constructions havingimproved resiliency as well as other advantageous properties, features,and benefits. The invention also encompasses golf balls containing theimproved core constructions.

SUMMARY OF THE INVENTION

The present invention provides a multi-piece golf ball comprising asolid core having three layers and a cover having at least one layer.The golf ball may have different constructions. For example, in oneversion, the multi-layered core includes: i) an inner core (center)comprising a foamed composition, wherein the inner core has a diameterin the range of about 0.100 to about 1.100 inches and a specific gravity(SG_(inner)): ii) an intermediate layer comprising a thermoplasticmaterial, wherein the intermediate layer is disposed about the innercore and has a thickness in the range of about 0.050 to about 0.400inches and a specific gravity (SG_(intermediate)); and iii) an outercore layer comprising a thermoset material, wherein the outer coverlayer is disposed about the intermediate core layer and has a thicknessin the range of about 0.200 to about 0.750 inches and a specific gravity(SG_(outer)). Preferably, the SG_(inner) is less than theSG_(intermediate) and SG_(outer). That is, the SG_(outer) is greaterthan the SG_(inner) and the SG_(intermediate) is greater than theSG_(inner).

Preferably, the inner core comprises a foam polyurethane compositionprepared from a mixture comprising polyisocyanate, polyol, and curingagent compounds, and blowing agent. Aromatic and aliphaticpolyisocyanates may be used. The foamed polyurethane composition may beprepared by using water as a blowing agent. The water is added to themixture in a sufficient amount to cause the mixture to foam. Surfactantsand catalysts, such as zinc and tin-based catalysts, may be included inthe mixture.

Different thermoplastic materials may be used to form the intermediatecore layer and different thermoset materials may be used to form theouter core layer in the present invention. In one preferred version, thethermoplastic material is non-foamed and the thermoset material isnon-foamed. For example, the thermoplastic material may be an ethyleneacid copolymer containing acid groups such that at least 70% of the acidgroups are neutralized; and the thermoset material may be polybutadienerubber. The intermediate and outer core layers may have differentthicknesses and properties. For example, the intermediate core layer mayhave a thickness in the range of about 0.070 to about 0.130 inches and aspecific gravity in the range of about 0.85 to about 3.10 g/cc. Inanother example, the outer core layer may have a thickness in the rangeof about 0.250 to about 0.750 inches and a specific gravity in the rangeof about 0.60 to about 2.90 g/cc.

The core layers may have different hardness gradients. For example, eachcore layer may have a positive, zero, or negative hardness gradient. Inone embodiment, the inner core has a positive hardness gradient; theintermediate core layer has a zero or negative hardness gradient; andthe outer core layer has a positive hardness gradient. In a secondembodiment, each of the core layers has a positive hardness gradient. Inyet another embodiment, the inner core has a positive hardness gradient;the intermediate core layer has a positive hardness gradient; and theouter core layer has a zero or negative hardness gradient. In analternative version, each of the inner; intermediate; and outer corelayers has a positive hardness gradient. In one preferred embodiment,the inner core has a positive hardness gradient, wherein the hardness ofthe geometric center (H_(inner core center)) is in the range of about 30to about 78 Shore C; and the hardness of the surface of the inner core(H_(inner core surface)) is in the range of about 46 to about 95 ShoreC. In one preferred embodiment, the inner core has a diameter in therange of about 0.100 to about 0.900 inches, for example 0.400 to 0.800inches; and a specific gravity in the range of about 0.25 to about 1.25g/cc, for example 0.30 to 0.95 g/cc.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are characteristic of the present invention areset forth in the appended claims. However, the preferred embodiments ofthe invention, together with further objects and attendant advantages,are best understood by reference to the following detailed descriptionin connection with the accompanying drawings in which:

FIG. 1 is a perspective view of a spherical inner core made of a foamedcomposition in accordance with the present invention;

FIG. 2 is a perspective view of one embodiment of upper and lower moldcavities used to make the multi-layered cores of the present invention;

FIG. 3 is a partial cut-away perspective view of a multi-layered corehaving inner, intermediate, and outer core layers made in accordancewith the present invention;

FIG. 4 is a cross-sectional view of a four-piece golf ball having amulti-layered core made in accordance with the present invention;

FIG. 5 is a cross-sectional view of a five-piece golf ball having amulti-layered core made in accordance with the present invention; and

FIG. 6 is a cross-sectional view of a six-piece golf ball having amulti-layered core made in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Golf Ball Constructions

Golf balls having various constructions may be made in accordance withthis invention. For example, golf balls having four-piece, five-piece,and six-piece constructions with single or multi-layered cover materialsmay be made. Representative illustrations of such golf ballconstructions are provided and discussed further below. The term,“layer” as used herein means generally any spherical portion of the golfball. More particularly, in one version, a four-piece golf ball having amulti-layered core and single-layered cover is made. The multi-layeredcore includes an inner core (center) and surrounding intermediate andouter core layers. In another version, a five-piece golf ball comprisinga multi-layered core and dual-cover (inner cover and outer cover layers)is made. In yet another construction, a six-piece golf ball having amulti-layered core; a casing layer, and cover layer(s) may be made. Asused herein, the term, “casing layer” means a layer of the ball disposedbetween the multi-layered core sub-assembly and cover. The casing layeralso may be referred to as a mantle or intermediate layer. The diameterand thickness of the different layers along with properties such ashardness and compression may vary depending upon the construction anddesired playing performance properties of the golf ball.

Inner Core Composition

In general, foam compositions are made by forming gas bubbles in apolymer mixture using a foaming (blowing) agent. As the bubbles form,the mixture expands and forms a foam composition that can be molded intoan end-use product having either an open or closed cellular structure.Flexible foams generally have an open cell structure, where the cellswalls are incomplete and contain small holes through which liquid andair can permeate. Such flexible foams are used for automobile seats,cushioning, mattresses, and the like. Rigid foams generally have aclosed cell structure, where the cell walls are continuous and complete,and are used for used for automobile panels and parts, buildinginsulation and the like.

In the present invention, the inner core (center) comprises a relativelyrigid and lightweight foam thermoplastic or thermoset polymercomposition. Referring to FIG. 1, a foamed inner core (4) having ageometric center (6) and outer skin (8) may be prepared in accordancewith this invention.

A wide variety of thermoplastic and thermoset materials may be used informing the foam composition of this invention including, for example,polyurethanes; polyureas; copolymers, blends and hybrids of polyurethaneand polyurea; olefin-based copolymer ionomer resins (for example,Surlyn® ionomer resins and DuPont HPF® 1000 and HPF® 2000, commerciallyavailable from DuPont; Iotek® ionomers, commercially available fromExxonMobil Chemical Company; Amplify® IO ionomers of ethylene acrylicacid copolymers, commercially available from Dow Chemical Company; andClarix® ionomer resins, commercially available from A. Schulman Inc.);polyethylene, including, for example, low density polyethylene, linearlow density polyethylene, and high density polyethylene; polypropylene;rubber-toughened olefin polymers; acid copolymers, for example,poly(meth)acrylic acid, which do not become part of an ionomericcopolymer; plastomers; flexomers; styrene/butadiene/styrene blockcopolymers; styrene/ethylene-butylene/styrene block copolymers;dynamically vulcanized elastomers; copolymers of ethylene and vinylacetates; copolymers of ethylene and methyl acrylates; polyvinylchloride resins; polyamides, poly(amide-ester) elastomers, and graftcopolymers of ionomer and polyamide including, for example, Pebax®thermoplastic polyether block amides, commercially available from ArkemaInc; cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, commercially available fromDuPont or RiteFlex®, commercially available from Ticona EngineeringPolymers; polyurethane-based thermoplastic elastomers, such asElastollan®, commercially available from BASF; synthetic or naturalvulcanized rubber; and combinations thereof. Castable polyurethanes,polyureas, and hybrids of polyurethanes-polyureas are particularlydesirable because these materials can be used to make a golf ball havinggood playing performance properties as discussed further below. By theterm, “hybrids of polyurethane and polyurea,” it is meant to includecopolymers and blends thereof.

Basically, polyurethane compositions contain urethane linkages formed bythe reaction of a multi-functional isocyanate containing two or more NCOgroups with a polyol having two or more hydroxyl groups (OH—OH)sometimes in the presence of a catalyst and other additives. Generally,polyurethanes can be produced in a single-step reaction (one-shot) or ina two-step reaction via a prepolymer or quasi-prepolymer. In theone-shot method, all of the components are combined at once, that is,all of the raw ingredients are added to a reaction vessel, and thereaction is allowed to take place. In the prepolymer method, an excessof polyisocyanate is first reacted with some amount of a polyol to formthe prepolymer which contains reactive NCO groups. This prepolymer isthen reacted again with a chain extender or curing agent polyol to formthe final polyurethane. Polyurea compositions, which are distinct fromthe above-described polyurethanes, also can be formed. In general,polyurea compositions contain urea linkages formed by reacting anisocyanate group (—N═C═O) with an amine group (NH or NH₂). Polyureas canbe produced in similar fashion to polyurethanes by either a one shot orprepolymer method. In forming a polyurea polymer, the polyol would besubstituted with a suitable polyamine. Hybrid compositions containingurethane and urea linkages also may be produced. For example, whenpolyurethane prepolymer is reacted with amine-terminated curing agentsduring the chain-extending step, any excess isocyanate groups in theprepolymer will react with the amine groups in the curing agent. Theresulting polyurethane-urea composition contains urethane and urealinkages and may be referred to as a hybrid. In another example, ahybrid composition may be produced when a polyurea prepolymer is reactedwith a hydroxyl-terminated curing agent. A wide variety of isocyanates,polyols, polyamines, and curing agents can be used to form thepolyurethane and polyurea compositions as discussed further below.

To prepare the foamed polyurethane, polyurea, or other polymercomposition, a foaming agent is introduced into the polymer formulation.In general, there are two types of foaming agents: physical foamingagents and chemical foaming agents.

Physical Foaming Agents.

These foaming agents typically are gasses that are introduced under highpressure directly into the polymer composition. Chlorofluorocarbons(CFCs) and partially halogenated chlorofluorocarbons are effective, butthese compounds are banned in many countries because of theirenvironmental side effects. Alternatively, aliphatic and cyclichydrocarbon gasses such as isobutene and pentane may be used. Inertgasses, such as carbon dioxide and nitrogen, also are suitable.

Chemical Foaming Agents.

These foaming agents typically are in the form of powder, pellets, orliquids and they are added to the composition, where they decompose orreact during heating and generate gaseous by-products (for example,nitrogen or carbon dioxide). The gas is dispersed and trapped throughoutthe composition and foams it.

Preferably, a chemical foaming agent is used to prepare the foamcompositions of this invention. Chemical blowing agents may beinorganic, such as ammonium carbonate and carbonates of alkalai metals,or may be organic, such as azo and diazo compounds, such asnitrogen-based azo compounds. Suitable azo compounds include, but arenot limited to, 2,2′-azobis(2-cyanobutane),2,2′-azobis(methylbutyronitrile), azodicarbonamide, p,p′-oxybis(benzenesulfonyl hydrazide), p-toluene sulfonyl semicarbazide, p-toluenesulfonyl hydrazide. Other foaming agents include any of the Celogens®sold by Crompton Chemical Corporation, and nitroso compounds,sulfonylhydrazides, azides of organic acids and their analogs,triazines, tri- and tetrazole derivatives, sulfonyl semicarbazides, ureaderivatives, guanidine derivatives, and esters such as alkoxyboroxines.Also, foaming agents that liberate gasses as a result of chemicalinteraction between components such as mixtures of acids and metals,mixtures of organic acids and inorganic carbonates, mixtures of nitrilesand ammonium salts, and the hydrolytic decomposition of urea may beused. Water is a preferred foaming agent. When added to the polyurethaneformulation, water will react with the isocyanate groups and formcarbamic acid intermediates. The carbamic acids readily decarboxylate toform an amine and carbon dioxide. The newly formed amine can thenfurther react with other isocyanate groups to form urea linkages and thecarbon dioxide forms the bubbles to produce the foam.

During the decomposition reaction of certain chemical foaming agents,more heat and energy is released than is needed for the reaction. Oncethe decomposition has started, it continues for a relatively long timeperiod. If these foaming agents are used, longer cooling periods aregenerally required. Hydrazide and azo-based compounds often are used asexothermic foaming agents. On the other hand, endothermic foaming agentsneed energy for decomposition. Thus, the release of the gasses quicklystops after the supply of heat to the composition has been terminated.If the composition is produced using these foaming agents, shortercooling periods are needed. Bicarbonate and citric acid-based foamingagents can be used as exothermic foaming agents.

Other suitable foaming agents include expandable gas-containingmicrospheres. Exemplary microspheres consist of an acrylonitrile polymershell encapsulating a volatile gas, such as isopentane gas. This gas iscontained within the sphere as a blowing agent. In their unexpandedstate, the diameter of these hollow spheres range from 10 to 17 μm andhave a true density of 1000 to 1300 kg/m³. When heated, the gas insidethe shell increases its pressure and the thermoplastic shell softens,resulting in a dramatic increase of the volume of the microspheres.Fully expanded, the volume of the microspheres will increase more than40 times (typical diameter values would be an increase from 10 to 40μm), resulting in a true density below 30 kg/m³ (0.25 lbs/gallon).Typical expansion temperatures range from 80-190° C. (176-374° F.). Suchexpandable microspheres are commercially available as Expancel® fromExpancel of Sweden or Akzo Nobel.

As an alternative to chemical and physical foaming agents or in additionto such foaming agents, as described above, other types of fillers thatlower the specific gravity of the composition can be used in accordancewith this invention. For example, polymeric, ceramic, and glass unfilledmicrospheres having a density of 0.1 to 1.0 g/cc and an average particlesize of 10 to 250 microns can be used to help lower specific gravity ofthe composition and achieve the desired density and physical properties.

Additionally, BASF polyurethane materials sold under the trade nameCellasto® and Elastocell®, microcellular polyurethanes, Elastopor® Hthat is a closed-cell polyurethane rigid foam, Elastoflex® W flexiblefoam systems, Elastoflex®E semiflexible foam systems, Elastofoam®flexible integrally-skinning systems, Elastolit®D/K/R integral rigidfoams, Elastopan®S, Elastollan® thermoplastic polyurethane elastomers(TPUs), and the like may be used in accordance with the presentinvention. Bayer also produces a variety of materials sold as Texin®TPUs, Baytec® and Vulkollan® elastomers, Baymer® rigid foams, Baydur®integral skinning foams, Bayfit®flexible foams available as castable,RIM grades, sprayable, and the like that may be used. Additional foammaterials that may be used herein include polyisocyanurate foams and avariety of “thermoplastic” foams, which may be cross-linked to varyingextents using free-radical (for example, peroxide) or radiationcross-linking (for example, UV, IR, Gamma, EB irradiation). Also, foamsmay be prepared from polybutadiene, polystyrene, polyolefin (includingmetallocene and other single site catalyzed polymers), ethylene vinylacetate (EVA), acrylate copolymers, such as EMA, EBA, Nucrel®-type acidco and terpolymers, ethylene propylene rubber (such as EPR, EPDM, andany ethylene copolymers), styrene-butadiene, and SEBS (any Kraton-type),PVC, PVDC, CPE (chlorinated polyethylene). Epoxy foams,urea-formaldehyde foams, latex foams and sponge, silicone foams,fluoropolymer foams and syntactic foams (hollow sphere filled) also maybe used.

In addition to the polymer and foaming agent, the foam composition alsomay include other ingredients such as, for example, cross-linkingagents, chain extenders, surfactants, dyes and pigments, coloringagents, fluorescent agents, adsorbents, stabilizers, softening agents,impact modifiers, antioxidants, antiozonants, and the like. Theformulations used to prepare the polyurethane foam compositions of thisinvention preferably contain a polyol, polyisocyanate, water, an amineor hydroxyl curing agent, surfactant, and a catalyst as describedfurther below.

Properties of Polyurethane Foams

The polyurethane foam compositions of this invention have numerouschemical and physical properties making them suitable for coreassemblies in golf balls. For example, there are properties relating tothe reaction of the isocyanate and polyol components and blowing agent,particularly “cream time,” “gel time,” “rise time,” “tack-free time,”and “free-rise density.” In general, cream time refers to the timeperiod from the point of mixing the raw ingredients together to thepoint where the mixture turns cloudy in appearance or changes color andbegins to rise from its initial stable state. Normally, the cream timeof the foam compositions of this invention is within the range of about20 to about 240 seconds. In general, gel time refers to the time periodfrom the point of mixing the raw ingredients together to the point wherethe expanded foam starts polymerizing/gelling. Rise time generallyrefers to the time period from the point of mixing the raw ingredientstogether to the point where the reacted foam has reached its largestvolume or maximum height. The rise time of the foam compositions of thisinvention typically is in the range of about 60 to about 360 seconds.Tack-free time generally refers to the time it takes for the reactedfoam to lose its tackiness, and the foam compositions of this inventionnormally have a tack-free time of about 60 to about 3600 seconds.Free-rise density refers to the density of the resulting foam when it isallowed to rise unrestricted without a cover or top being placed on themold.

The density of the foam is an important property and is defines as theweight per unit volume (typically, kg/m³ or lb/ft³ or g/cm³) and can bemeasured per ASTM D-1622. The hardness, stiffness, and load-bearingcapacity of the foam are independent of the foam's density, althoughfoams having a high density typically have high hardness and stiffness.Normally, foams having higher densities have higher compressionstrength. Surprisingly, the foam compositions used to produce the innercore of the golf balls per this invention have a relatively low density;however, the foams are relatively firm. Tensile strength,tear-resistance, and elongation generally refer to the foam's ability toresist breaking or tearing, and these properties can be measured perASTM D-1623. The durability of foams is important, because introducingfillers and other additives into the foam composition can increase thetendency of the foam to break or tear apart. In general, the tensilestrength of the foam compositions of this invention is in the range ofabout 20 to about 1000 psi (parallel to the foam rise) and about 50 toabout 1000 psi (perpendicular to the foam rise) as measured per ASTMD-1623 at 23° C. and 50% relative humidity (RH). Meanwhile, the flexmodulus of the foams of this invention is generally in the range ofabout 5 to about 45 kPa as measured per ASTM D-790, and the foamsgenerally have a compressive modulus of 200 to 50,000 psi.

In another test, compression strength is measured on an Instron machineaccording to ASTM D-1621. The foam is cut into blocks and thecompression strength is measured as the force required to compress theblock by 10%. In general, the compressive strength of the foamcompositions of this invention is in the range of about 100 to about1800 psi (parallel and perpendicular to the foam rise) as measured perASTM D-1621 at 23° C. and 50% relative humidity (RH). The test isconducted perpendicular to the rise of the foam or parallel to the riseof the foam. The Percentage (%) of Compression Set also can be used.This is a measure of the permanent deformation of a foam sample after ithas been compressed between two metal plates under controlled time andtemperature condition (standard—22 hours at 70° C. (158° F.)). The foamis compressed to a thickness given as a percentage of its originalthickness that remained “set.” Preferably, the Compression Set of thefoam is less than ten percent (10%), that is, the foam recovers to apoint of 90% or greater of its original thickness.

Methods of Preparing the Foam Composition

The foam compositions of this invention may be prepared using differentmethods. In one preferred embodiment, the method involves preparing acastable composition comprising a reactive mixture of a polyisocyanate,polyol, water, curing agent, surfactant, and catalyst. A motorized mixercan be used to mix the starting ingredients together and form a reactiveliquid mixture. Alternatively, the ingredients can be manually mixedtogether. An exothermic reaction occurs when the ingredients are mixedtogether and this continues as the reactive mixture is dispensed intothe mold cavities (otherwise referred to as half-molds or mold cups).The mold cavities may be referred to as first and second, or upper andlower, mold cavities. The mold cavities preferably are made of metalsuch as, for example, brass or silicon bronze.

Referring to FIG. 2, the mold cavities are generally indicated at (9)and (10). The lower and upper mold cavities (9, 10) are placed in lowerand upper mold frame plates (11, 12). The frame plates (11, 12) containguide pins and complementary alignment holes (not shown in drawing). Theguide pins are inserted into the alignment holes to secure the lowerplate (11) to the upper plate (12). The lower and upper mold cavities(9, 10) are mated together as the frame plates (11, 12) are fastened.When the lower and upper mold cavities (9, 10) are joined together, theydefine an interior spherical cavity that houses the spherical core. Theupper mold contains a vent or hole (14) to allow for the expanding foamto fill the cavities uniformly. A secondary overflow chamber (16), whichis located above the vent (14), can be used to adjust the amount of foamoverflow and thus adjust the density of the core structure being moldedin the cavities. As the lower and upper mold cavities (9, 10) are matedtogether and sufficient heat and pressure is applied, the foamedcomposition cures and solidifies to form a relatively rigid andlightweight spherical core. The resulting cores are cooled and thenremoved from the mold.

Hardness of the Inner Core

As shown in FIG. 1, a foamed inner core (4) having a geometric center(6) and outer skin (8) may be prepared per the molding method discussedabove. The outer skin (8) is generally a non-foamed region that formsthe outer surface of the core structure. The resulting inner corepreferably has a diameter within a range of about 0.100 to about 1.100inches. For example, the inner core may have a diameter within a rangeof about 0.250 to about 1.000 inches. In another example, the inner coremay have a diameter within a range of about 0.300 to about 0.800 inches.More particularly, the inner core preferably has a diameter size with alower limit of about 0.10 or 0.12 or 0.15 or 0.25 or 0.30 or 0.35 or0.45 or 0.55 inches and an upper limit of about 0.60 or 0.65 or 0.70 or0.80 or 0.90 or 1.00 or 1.10 inches. The outer skin (8) of the innercore is relatively thin preferably having a thickness of less than about0.020 inches and more preferably less than 0.010 inches. In onepreferred embodiment, the foamed core has a “positive” hardness gradient(that is, the outer skin of the inner core is harder than its geometriccenter.)

For example, the geometric center hardness of the inner core(H_(inner core center)), as measured in Shore C units, is about 10 ShoreC or greater and preferably has a lower limit of about 10 or 16 or 20 or25 or 30 or 32 or 34 or 36 or 40 Shore C and an upper limit of about 42or 44 or 48 or 50 or 52 or 56 or 60 or 62 or 65 or 68 or 70 or 74 or 78or 80 Shore C. In one preferred version, the geometric center hardnessof the inner core (H_(inner core center)) is about 60 Shore C. TheH_(inner core center), as measured in Shore D units, is about 15 Shore Dor greater and more preferably within a range having a lower limit ofabout 15 or 18 or 20 or 22 or 25 or 28 or 30 or 32 or 36 or 40 or 44Shore D and an upper limit of about 45 or 48 or 50 or 52 or 55 or 58 or60 or 62 or 64 or 66 or 70 or 72 or 74 or 78 or 80 or 82 or 84 or 88 or90 Shore D. Meanwhile, the outer surface hardness of the inner core(H_(inner core surface)), as measured in Shore C, is about 20 Shore C orgreater and preferably has a lower limit of about 20 or 22 or 24 or 28or 30 or 32 or 35 or 36 or 40 or 42 or 44 or 48 or 50 Shore C and anupper limit of about 52 or 55 or 58 or 60 or 62 or 64 or 66 or 70 or 74or 78 or 80 or 86 or 88 or 90 or 92 or 95 Shore C. The outer surfacehardness of the inner core ((H_(inner core surface)), as measured inShore D units, preferably has a lower limit of about 25 or 28 or 30 or32 or 36 or 40 or 44 Shore D and an upper limit of about 45 or 48 or 50or 52 or 55 or 58 or 60 or 62 or 64 or 66 or 70 or 74 or 78 or 80 or 82or 84 or 88 or 90 or 94 or 96 Shore D.

Density of the Inner Core

The foamed inner core preferably has a specific gravity of about 0.25 toabout 1.25 g/cc. That is, the density of the inner core (as measured atany point of the inner core structure) is preferably within the range ofabout 0.25 to about 1.25 g/cc. By the term, “specific gravity of theinner core” (“SG_(inner)”), it is generally meant the specific gravityof the inner core as measured at any point of the inner core structure.It should be understood, however, that the specific gravity values, astaken at different points of the inner core structure, may vary. Forexample, the foamed inner core may have a “positive” density gradient(that is, the outer surface (skin) of the inner core may have a densitygreater than the geometric center of the inner core.) In one preferredversion, the specific gravity of the geometric center of the inner core(SG_(center of inner core)) is less than 1.00 g/cc and more preferably0.90 g/cc or less. More particularly, in one version, the(SG_(center of inner core)) is in the range of about 0.10 to about 0.90g/cc. For example, the (SG_(center) of inner core) may be within a rangehaving a lower limit of about 0.10 or 0.15 of 0.20 or 0.24 or 0.30 or0.35 or 0.37 or 0.40 or 0.42 or 0.45 or 0.47 or 0.50 and an upper limitof about 0.60 or 0.65 or 0.70 or 0.74 or 0.78 or 0.80, or 0.82 or 0.84or 0.85 or 0.88 or 0.90 g/cc. Meanwhile, the specific gravity of theouter surface (skin) of the inner core (SG_(skin of inner core)), in onepreferred version, is greater than about 0.90 g/cc and more preferablygreater than 1.00 g/cc. For example, the (SG_(skin of inner core)) mayfall within the range of about 0.90 to about 2.00. More particularly, inone version, the (SG_(skin of inner core)) may have a specific gravitywith a lower limit of about 0.90 or 0.92 or 0.95 or 0.98 or 1.00 or 1.02or 1.06 or 1.10 or 1.12 or 1.15 or 1.18 and an upper limit of about 1.20or 1.24 or 1.30 or 1.32 or 1.35 or 1.38 or 1.40 or 1.44 or 1.50 or 1.60or 1.65 or 1.70 or 1.76 or 1.80 or 1.90 or 1.92 or 2.00. In otherinstances, the outer skin may have a specific gravity of less than 0.90g/cc. For example, the specific gravity of the outer skin(SG_(skin of inner core)) may be about 0.75 or 0.80 or 0.82 or 0.85 or0.88 g/cc. In such instances, wherein both the(SG_(center of inner core)) and (SG_(skin of inner core)) are less than0.90 g/cc, it is still preferred that the (SG_(center of inner core)) isless than the (SG_(skin of inner core)).

Polyisocyanates and Polyols for Making the Polyurethane Foams

As discussed above, in one preferred embodiment, a foamed polyurethanecomposition is used to form the inner core. In general, the polyurethanecompositions contain urethane linkages formed by reacting an isocyanategroup (—N═C═O) with a hydroxyl group (OH). The polyurethanes areproduced by the reaction of multi-functional isocyanates containing twoor more isocyanate groups with a polyol having two or more hydroxylgroups. The formulation may also contain a catalyst, surfactant, andother additives.

In particular, the foam inner core of this invention may be preparedfrom a composition comprising an aromatic polyurethane, which ispreferably formed by reacting an aromatic diisocyanate with a polyol.Suitable aromatic diisocyanates that may be used in accordance with thisinvention include, for example, toluene 2,4-diisocyanate (TDI), toluene2,6-diisocyanate (TDI), 4,4′-methylene diphenyl diisocyanate (MDI),2,4′-methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyldiisocyanate (PMDI), p-phenylene diisocyanate (PPDI), m-phenylenediisocyanate (PDI), naphthalene 1,5-diisocyanate (NDI), naphthalene2,4-diisocyanate (NDI), p-xylene diisocyanate (XDI), and homopolymersand copolymers and blends thereof. The aromatic isocyanates are able toreact with the hydroxyl or amine compounds and form a durable and toughpolymer having a high melting point. The resulting polyurethanegenerally has good mechanical strength and tear-resistance.

Alternatively, the foamed composition of the inner core may be preparedfrom a composition comprising aliphatic polyurethane, which ispreferably formed by reacting an aliphatic diisocyanate with a polyol.Suitable aliphatic diisocyanates that may be used in accordance withthis invention include, for example, isophorone diisocyanate (IPDI),1,6-hexamethylene diisocyanate (HDI), 4,4′-dicyclohexylmethanediisocyanate (“H₁₂ MDI”), meta-tetramethylxylyene diisocyanate (TMXDI),trans-cyclohexane diisocyanate (CHDI),1,3-bis(isocyanatomethyl)cyclohexane;1,4-bis(isocyanatomethyl)cyclohexane; and homopolymers and copolymersand blends thereof. The resulting polyurethane generally has good lightand thermal stability. Preferred polyfunctional isocyanates include4,4′-methylene diphenyl diisocyanate (MDI), 2,4′-methylene diphenyldiisocyanate (MDI), and polymeric MDI having a functionality in therange of 2.0 to 3.5 and more preferably 2.2 to 2.5.

Any suitable polyol may be used to react with the polyisocyanate inaccordance with this invention. Exemplary polyols include, but are notlimited to, polyether polyols, hydroxy-terminated polybutadiene(including partially/fully hydrogenated derivatives), polyester polyols,polycaprolactone polyols, and polycarbonate polyols. In one preferredembodiment, the polyol includes polyether polyol. Examples include, butare not limited to, polytetramethylene ether glycol (PTMEG),polyethylene propylene glycol, polyoxypropylene glycol, and mixturesthereof. The hydrocarbon chain can have saturated or unsaturated bondsand substituted or unsubstituted aromatic and cyclic groups. Preferably,the polyol of the present invention includes PTMEG.

As discussed further below, chain extenders (curing agents) are added tothe mixture to build-up the molecular weight of the polyurethanepolymer. In general, hydroxyl-terminated curing agents, amine-terminatedcuring agents, and mixtures thereof are used.

A catalyst may be employed to promote the reaction between theisocyanate and polyol compounds. Suitable catalysts include, but are notlimited to, bismuth catalyst; zinc octoate; tin catalysts such asbis-butyltin dilaurate, bis-butyltin diacetate, stannous octoate; tin(II) chloride, tin (IV) chloride, bis-butyltin dimethoxide,dimethyl-bis[1-oxonedecyl)oxy]stannane, di-n-octyltin bis-isooctylmercaptoacetate; amine catalysts such as triethylenediamine,triethylamine, tributylamine, 1,4-diaza(2,2,2)bicyclooctane,tetramethylbutane diamine, bis[2-dimethylaminoethyl]ether,N,N-dimethylaminopropylamine, N,N-dimethylcyclohexylamine,N,N,N′,N′,N″-pentamethyldiethylenetriamine, diethanolamine,dimethtlethanolamine, N-[2-(dimethylamino)ethyl]-N-methylethanolamine,N-ethylmorpholine, 3-dimethylamino-N,N-dimethylpropionamide, andN,N′,N″-dimethylaminopropylhexahydrotriazine; organic acids such asoleic acid and acetic acid; delayed catalysts; and mixtures thereof.Zirconium-based catalysts such as, for example, bis(2-dimethylaminoethyl) ether; mixtures of zinc complexes and amine compounds suchas KKAT™ XK 614, available from King Industries; and amine catalystssuch as Niax™ A-2 and A-33, available from Momentive SpecialtyChemicals, Inc. are particularly preferred. The catalyst is preferablyadded in an amount sufficient to catalyze the reaction of the componentsin the reactive mixture. In one embodiment, the catalyst is present inan amount from about 0.001 percent to about 1 percent, and preferably0.1 to 0.5 percent, by weight of the composition.

In one preferred embodiment, as described above, water is used as thefoaming agent—the water reacts with the polyisocyanate compound(s) andforms carbon dioxide gas which induces foaming of the mixture. Thereaction rate of the water and polyisocyanate compounds affects howquickly the foam is formed as measured per reaction profile propertiessuch as cream time, gel time, and rise time of the foam.

The hydroxyl chain-extending (curing) agents are preferably selectedfrom the group consisting of ethylene glycol; diethylene glycol;polyethylene glycol; propylene glycol; 2-methyl-1,3-propanediol;2-methyl-1,4-butanediol; monoethanolamine; diethanolamine;triethanolamine; monoisopropanolamine; diisopropanolamine; dipropyleneglycol; polypropylene glycol; 1,2-butanediol; 1,3-butanediol;1,4-butanediol; 2,3-butanediol; 2,3-dimethyl-2,3-butanediol;trimethylolpropane; cyclohexyldimethylol; triisopropanolamine;N,N,N′,N′-tetra-(2-hydroxypropyl)-ethylene diamine; diethylene glycolbis-(aminopropyl) ether; 1,5-pentanediol; 1,6-hexanediol;1,3-bis-(2-hydroxyethoxy) cyclohexane; 1,4-cyclohexyldimethylol;1,3-bis-[2-(2-hydroxyethoxyl)ethoxy]cyclohexane;1,3-bis-{2-[2-(2-hydroxyethoxyl)ethoxy]ethoxy}cyclohexane;trimethylolpropane; polytetramethylene ether glycol (PTMEG), preferablyhaving a molecular weight from about 250 to about 3900; and mixturesthereof. Di, tri, and tetra-functional polycaprolactone diols such as,2-oxepanone polymer initiated with 1,4-butanediol,2-ethyl-2-(hydroxymethyl)-1,3-propanediol, or2,2-bis(hydroxymethyl)-1,3-propanediolsuch, may be used.

Suitable amine chain-extending (curing) agents that can be used inchain-extending the polyurethane prepolymer include, but are not limitedto, unsaturated diamines such as 4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-dianiline or “MDA”), m-phenylenediamine,p-phenylenediamine, 1,2- or 1,4-bis(sec-butylamino)benzene,3,5-diethyl-(2,4- or 2,6-) toluenediamine or “DETDA”,3,5-dimethylthio-(2,4- or 2,6-)toluenediamine, 3,5-diethylthio-(2,4- or2,6-)toluenediamine, 3,3′-dimethyl-4,4′-diamino-diphenylmethane,3,3′-diethyl-5,5′-dimethyl4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-ethyl-6-methyl-benezeneamine)),3,3′-dichloro-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-chloroaniline) or “MOCA”),3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2,6-diethylaniline),2,2′-dichloro-3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(3-chloro-2,6-diethyleneaniline) or “MCDEA”),3,3′-diethyl-5,5′-dichloro-4,4′-diamino-diphenylmethane, or “MDEA”),3,3′-dichloro-2,2′,6,6′-tetraethyl-4,4′-diamino-diphenylmethane,3,3′-dichloro-4,4′-diamino-diphenylmethane,4,4′-methylene-bis(2,3-dichloroaniline) (i.e.,2,2′,3,3′-tetrachloro-4,4′-diamino-diphenylmethane or “MDCA”),4,4′-bis(sec-butylamino)-diphenylmethane,N,N′-dialkylamino-diphenylmethane,trimethyleneglycol-di(p-aminobenzoate),polyethyleneglycol-di(p-aminobenzoate),polytetramethyleneglycol-di(p-aminobenzoate); saturated diamines such asethylene diamine, 1,3-propylene diamine, 2-methyl-pentamethylenediamine, hexamethylene diamine, 2,2,4- and 2,4,4-trimethyl-1,6-hexanediamine, imino-bis(propylamine), imido-bis(propylamine),methylimino-bis(propylamine) (i.e.,N-(3-aminopropyl)-N-methyl-1,3-propanediamine),1,4-bis(3-aminopropoxy)butane (i.e.,3,3′-[1,4-butanediylbis-(oxy)bis]-1-propanamine),diethyleneglycol-bis(propylamine) (i.e.,diethyleneglycol-di(aminopropyl)ether),4,7,10-trioxatridecane-1,13-diamine, 1-methyl-2,6-diamino-cyclohexane,1,4-diamino-cyclohexane, poly(oxyethylene-oxypropylene) diamines, 1,3-or 1,4-bis(methylamino)-cyclohexane, isophorone diamine, 1,2- or1,4-bis(sec-butylamino)-cyclohexane, N,N′-diisopropyl-isophoronediamine, 4,4′-diamino-dicyclohexylmethane,3,3′-dimethyl-4,4′-diamino-dicyclohexylmethane,3,3′-dichloro-4,4′-diamino-dicyclohexylmethane,N,N′-dialkylamino-dicyclohexylmethane, polyoxyethylene diamines,3,3′-diethyl-5,5′-dimethyl-4,4′-diamino-dicyclohexylmethane,polyoxypropylene diamines,3,3′-diethyl-5,5′-dichloro-4,4′-diamino-dicyclohexylmethane,polytetramethylene ether diamines,3,3′,5,5′-tetraethyl-4,4′-diamino-dicyclohexylmethane (i.e.,4,4′-methylene-bis(2,6-diethylaminocyclohexane)),3,3′-dichloro-4,4′-diamino-dicyclohexylmethane,2,2′-dichloro-3,3′,5,5′-tetraethyl-4,4′-diamino-dicyclohexylmethane,(ethylene oxide)-capped polyoxypropylene ether diamines,2,2′,3,3′-tetrachloro-4,4′-diamino-dicyclohexylmethane,4,4′-bis(sec-butylamino)-dicyclohexylmethane; triamines such asdiethylene triamine, dipropylene triamine, (propylene oxide)-basedtriamines (i.e., polyoxypropylene triamines),N-(2-aminoethyl)-1,3-propylenediamine (i.e., N₃-amine), glycerin-basedtriamines, (all saturated); tetramines such asN,N′-bis(3-aminopropyl)ethylene diamine (i.e., N₄-amine) (bothsaturated), triethylene tetramine; and other polyamines such astetraethylene pentamine (also saturated). One suitable amine-terminatedchain-extending agent is Ethacure 300™ (dimethylthiotoluenediamine or amixture of 2,6-diamino-3,5-dimethylthiotoluene and2,4-diamino-3,5-dimethylthiotoluene.) The amine curing agents used aschain extenders normally have a cyclic structure and a low molecularweight (250 or less).

When a hydroxyl-terminated curing agent is used, the resultingpolyurethane composition contains urethane linkages. On the other hand,when an amine-terminated curing agent is used, any excess isocyanategroups will react with the amine groups in the curing agent. Theresulting polyurethane composition contains urethane and urea linkagesand may be referred to as a polyurethane/urea hybrid.

Intermediate Core Layer Composition

As discussed above, the inner core is made preferably from a foamedcomposition. The intermediate core layer, meanwhile, is formedpreferably from a non-foamed thermoplastic composition. Moreparticularly, the intermediate core layer is formed preferably from anionomer composition comprising an ethylene acid copolymer containingacid groups that are at least partially neutralized. Preferably, theneutralization level is greater than 70%, more preferably at least 90%and even more preferably at least 100%. Suitable ethylene acidcopolymers that may be used to form the compositions of this inventionare generally referred to as copolymers of ethylene; C₃ to C₈ α,β-ethylenically unsaturated mono- or dicarboxylic acid; and optionalsoftening monomer. Copolymers may include, without limitation, ethyleneacid copolymers, such as ethylene/(meth)acrylic acid,ethylene/(meth)acrylic acid/maleic anhydride, ethylene/(meth)acrylicacid/maleic acid mono-ester, ethylene/maleic acid, ethylene/maleic acidmono-ester, ethylene/(meth)acrylic acid/n-butyl (meth)acrylate,ethylene/(meth)acrylic acid/iso-butyl (meth)acrylate,ethylene/(meth)acrylic acid/methyl (meth)acrylate,ethylene/(meth)acrylic acid/ethyl (meth)acrylate terpolymers, and thelike. The term, “copolymer,” as used herein, includes polymers havingtwo types of monomers, those having three types of monomers, and thosehaving more than three types of monomers. Preferred α, β-ethylenicallyunsaturated mono- or dicarboxylic acids are (meth) acrylic acid,ethacrylic acid, maleic acid, crotonic acid, fumaric acid, itaconicacid. (Meth) acrylic acid is most preferred. As used herein, “(meth)acrylic acid” means methacrylic acid and/or acrylic acid. Likewise,“(meth) acrylate” means methacrylate and/or acrylate.

When a softening monomer is included, such copolymers are referred toherein as E/X/Y-type copolymers, wherein E is ethylene; X is a C₃ to C₈α, β-ethylenically unsaturated mono- or dicarboxylic acid; and Y is asoftening monomer. The softening monomer is typically an alkyl (meth)acrylate, wherein the alkyl groups have from 1 to 8 carbon atoms.Preferred E/X/Y-type copolymers are those wherein X is (meth) acrylicacid and/or Y is selected from (meth) acrylate, n-butyl (meth) acrylate,isobutyl (meth) acrylate, methyl (meth) acrylate, and ethyl (meth)acrylate. More preferred E/X/Y-type copolymers are ethylene/(meth)acrylic acid/n-butyl acrylate, ethylene/(meth) acrylic acid/methylacrylate, and ethylene/(meth) acrylic acid/ethyl acrylate.

The amount of ethylene in the acid copolymer is typically at least 15wt. %, preferably at least 25 wt. %, more preferably least 40 wt. %, andeven more preferably at least 60 wt. %, based on total weight of thecopolymer. The amount of C₃ to C₈ α, β-ethylenically unsaturated mono-or dicarboxylic acid in the acid copolymer is typically from 1 wt. % to35 wt. %, preferably from 5 wt. % to 30 wt. %, more preferably from 5wt. % to 25 wt. %, and even more preferably from 10 wt. % to 20 wt. %,based on total weight of the copolymer. The amount of optional softeningcomonomer in the acid copolymer is typically from 0 wt. % to 50 wt. %,preferably from 5 wt. % to 40 wt. %, more preferably from 10 wt. % to 35wt. %, and even more preferably from 20 wt. % to 30 wt. %, based ontotal weight of the copolymer. “Low acid” and “high acid” ionomericpolymers, as well as blends of such ionomers, may be used. In general,low acid ionomers are considered to be those containing 16 wt. % or lessof acid moieties, whereas high acid ionomers are considered to be thosecontaining greater than 16 wt. % of acid moieties.

The acidic groups in the copolymeric ionomers are partially or totallyneutralized with a cation source. Suitable cation sources include metalcations and salts thereof, organic amine compounds, ammonium, andcombinations thereof. Preferred cation sources are metal cations andsalts thereof, wherein the metal is preferably lithium, sodium,potassium, magnesium, calcium, barium, lead, tin, zinc, aluminum,manganese, nickel, chromium, copper, or a combination thereof. The metalcation salts provide the cations capable of neutralizing (at varyinglevels) the carboxylic acids of the ethylene acid copolymer and fattyacids, if present, as discussed further below. These include, forexample, the sulfate, carbonate, acetate, oxide, or hydroxide salts oflithium, sodium, potassium, magnesium, calcium, barium, lead, tin, zinc,aluminum, manganese, nickel, chromium, copper, or a combination thereof.Preferred metal cation salts are calcium and magnesium-based salts. Highsurface area cation particles such as micro and nano-scale cationparticles are preferred. The amount of cation used in the composition isreadily determined based on desired level of neutralization.

For example, ionomeric resins having acid groups that are neutralizedfrom about 10 percent to about 100 percent may be used. In one ionomercomposition, the acid groups are partially neutralized. That is, theneutralization level is from about 10% to about 70%, more preferably 20%to 60%, and most preferably 30 to 50%. These ionomer compositions,containing acid groups neutralized to 70% or less, may be referred toionomers having relatively low neutralization levels.

On the other hand, the ionomer composition may contain acid groups thatare highly or fully-neutralized. These highly neutralized polymers(HNPs) are preferred for forming at least one core layer in the presentinvention. In these HNPs, the neutralization level is greater than 70%,preferably at least 90% and even more preferably at least 100%. Inanother embodiment, an excess amount of neutralizing agent, that is, anamount greater than the stoichiometric amount needed to neutralize theacid groups, may be used. That is, the acid groups may be neutralized to100% or greater, for example 110% or 120% or greater. In one preferredembodiment, a high acid ethylene acid copolymer containing about 19 to20 wt. % methacrylic or acrylic acid is neutralized with zinc and sodiumcations to a 95% neutralization level.

“Ionic plasticizers” such as organic acids or salts of organic acids,particularly fatty acids, may be added to the ionomer resin if needed.Such ionic plasticizers are used to make conventional ionomercomposition more processable as described in Rajagopalan et al., U.S.Pat. No. 6,756,436, the disclosure of which is hereby incorporated byreference. In one preferred embodiment, the thermoplastic ionomercomposition, containing acid groups neutralized to 70% or less, does notinclude a fatty acid or salt thereof, or any other ionic plasticizer. Onthe other hand, the thermoplastic ionomer composition, containing acidgroups neutralized to greater than 70%, includes an ionic plasticizer,particularly a fatty acid or salt thereof. For example, the ionicplasticizer may be added in an amount of 0.5 to 10 pph, more preferably1 to 5 pph. The organic acids may be aliphatic, mono- ormulti-functional (saturated, unsaturated, or multi-unsaturated) organicacids. Salts of these organic acids may also be employed. Suitable fattyacid salts include, for example, metal stearates, laureates, oleates,palmitates, pelargonates, and the like. For example, fatty acid saltssuch as zinc stearate, calcium stearate, magnesium stearate, bariumstearate, and the like can be used. The salts of fatty acids aregenerally fatty acids neutralized with metal ions. The metal cationsalts provide the cations capable of neutralizing (at varying levels)the carboxylic acid groups of the fatty acids. Examples include thesulfate, carbonate, acetate and hydroxide salts of metals such asbarium, lithium, sodium, zinc, bismuth, chromium, cobalt, copper,potassium, strontium, titanium, tungsten, magnesium, cesium, iron,nickel, silver, aluminum, tin, or calcium, and blends thereof. It ispreferred the organic acids and salts be relatively non-migratory (theydo not bloom to the surface of the polymer under ambient temperatures)and non-volatile (they do not volatilize at temperatures required formelt-blending).

As noted above, the final ionomer compositions may contain additionalmaterials such as, for example, a small amount of ionic plasticizer,which is particularly effective at improving the processability ofhighly-neutralized ionomers. For example, the ionic plasticizer may beadded in an amount of 0.5 to 10 pph, more preferably 1 to 5 pph. Inaddition to the fatty acids and salts of fatty acids discussed above,other suitable ionic plasticizers include, for example, polyethyleneglycols, waxes, bis-stearamides, minerals, and phthalates. In anotherembodiment, an amine or pyridine compound is used, preferably inaddition to a metal cation. Suitable examples include, for example,ethylamine, methylamine, diethylamine, tert-butylamine, dodecylamine,and the like.

The ionomer compositions may contain a wide variety of fillers and someof these fillers may be used to adjust the specific gravity of thecomposition as needed. High surface-area fillers that have an affinityfor the acid groups in ionomer may be used. In particular, fillers suchas particulate, fibers, or flakes having cationic nature such that theymay also contribute to the neutralization of the ionomer are suitable.For example, aluminum oxide, zinc oxide, tin oxide, barium sulfate, zincsulfate, calcium oxide, calcium carbonate, zinc carbonate, bariumcarbonate, tungsten, tungsten carbide, and lead silicate fillers may beused. Also, silica, fumed silica, and precipitated silica, such as thosesold under the tradename, HISIL™, from PPG Industries, carbon black,carbon fibers, and nano-scale materials such as nanotubes, nanoflakes,nanofillers, and nanoclays may be used. Relatively heavy-weight fillersalso may be added to the ionomer compositions including, but not limitedto, particulate, powders, fibers and flakes of heavy metals such ascopper, nickel, tungsten, brass, steel, magnesium, molybdenum, cobalt,lead, tin, silver, gold, and platinum, and alloys thereof. Steelmaterials also can be added. In other instances, it may be desirable toadd relatively light-weight metals such as titanium and aluminum alloysthereof. Other additives and fillers include, but are not limited to,chemical blowing and foaming agents, optical brighteners, coloringagents, fluorescent agents, whitening agents, UV absorbers, lightstabilizers, defoaming agents, processing aids, antioxidants,stabilizers, softening agents, fragrance components, plasticizers,impact modifiers, titanium dioxide, acid copolymer wax, surfactants,rubber regrind (recycled core material), clay, mica, talc, glass flakes,milled glass, and mixtures thereof. Suitable additives are more fullydescribed in, for example, Rajagopalan et al., U.S. Patent ApplicationPublication No. 2003/0225197, the entire disclosure of which is herebyincorporated herein by reference. In a particular embodiment, the totalamount of additive(s) and filler(s) present in the final thermoplasticionomeric composition is 25 wt. % or less, or 20 wt. % or less, or 15wt. % or less, or 12 wt. % or less, or 10 wt. % or less, or 9 wt. % orless, or 6 wt. % or less, or 5 wt. % or less, or 4 wt. % or less, or 3wt. % or less, based on total weight of the ionomeric composition.

The ethylene acid copolymer is used in an amount of at least about 5% byweight based on total weight of composition and is generally present inan amount of about 5% to about 100%, or an amount within a range havinga lower limit of 5% or 10% or 20% or 30% or 40% or 50% and an upperlimit of 55% or 60% or 70% or 80% or 90% or 95% or 100%. Preferably, theconcentration of ethylene acid copolymer is about 40 to about 95 weightpercent.

Other suitable thermoplastic polymers that may be used to form theintermediate core layer include, but are not limited to, the followingpolymers (including homopolymers, copolymers, and derivatives thereof.)

(a) polyesters, particularly those modified with a compatibilizing groupsuch as sulfonate or phosphonate, including modified poly(ethyleneterephthalate), modified poly(butylene terephthalate), modifiedpoly(propylene terephthalate), modified poly(trimethyleneterephthalate), modified poly(ethylene naphthenate), and those disclosedin U.S. Pat. Nos. 6,353,050, 6,274,298, and 6,001,930, the entiredisclosures of which are hereby incorporated herein by reference, andblends of two or more thereof;

(b) polyamides, polyamide-ethers, and polyamide-esters, and thosedisclosed in U.S. Pat. Nos. 6,187,864, 6,001,930, and 5,981,654, theentire disclosures of which are hereby incorporated herein by reference,and blends of two or more thereof;

(c) polyurethanes, polyureas, polyurethane-polyurea hybrids, and blendsof two or more thereof;

(d) fluoropolymers, such as those disclosed in U.S. Pat. Nos. 5,691,066,6,747,110 and 7,009,002, the entire disclosures of which are herebyincorporated herein by reference, and blends of two or more thereof;

(e) polystyrenes, such as poly(styrene-co-maleic anhydride),acrylonitrile-butadiene-styrene, poly(styrene sulfonate), polyethylenestyrene, and blends of two or more thereof;

(f) polyvinyl chlorides and grafted polyvinyl chlorides, and blends oftwo or more thereof;

(g) polycarbonates, blends ofpolycarbonate/acrylonitrile-butadiene-styrene, blends ofpolycarbonate/polyurethane, blends of polycarbonate/polyester, andblends of two or more thereof;

(h) polyethers, such as polyarylene ethers, polyphenylene oxides, blockcopolymers of alkenyl aromatics with vinyl aromatics and polyamicesters,and blends of two or more thereof;

(i) polyimides, polyetherketones, polyamideimides, and blends of two ormore thereof; and

(j) polycarbonate/polyester copolymers and blends.

These thermoplastic polymers may be used by and in themselves to formthe intermediate core layer, or blends of thermoplastic polymersincluding the above-described polymers and ethylene acid copolymerionomers may be used. It also is recognized that the ionomercompositions may contain a blend of two or more ionomers. For example,the composition may contain a 50/50 wt. % blend of two differenthighly-neutralized ethylene/methacrylic acid copolymers. In anotherversion, the composition may contain a blend of one or more ionomers anda maleic anhydride-grafted non-ionomeric polymer. The non-ionomericpolymer may be a metallocene-catalyzed polymer. In another version, thecomposition contains a blend of a highly-neutralizedethylene/methacrylic acid copolymer and a maleic anhydride-graftedmetallocene-catalyzed polyethylene. In yet another version, thecomposition contains a material selected from the group consisting ofhighly-neutralized ionomers optionally blended with a maleicanhydride-grafted non-ionomeric polymer; polyester elastomers; polyamideelastomers; and combinations of two or more thereof.

Outer Core Layer Composition

As discussed above, the outer core layer is formed preferably from anon-foamed thermoset material. Suitable thermoset rubber materials thatmay be used to make the outer core layer include, but are not limitedto, polybutadiene, polyisoprene, ethylene propylene rubber (“EPR”),ethylene-propylene-diene (“EPDM”) rubber, styrene-butadiene rubber,styrenic block copolymer rubbers (such as “SI”, “SIS”, “SB”, “SBS”,“SIBS”, and the like, where “S” is styrene, “I” is isobutylene, and “B”is butadiene), polyalkenamers such as, for example, polyoctenamer, butylrubber, halobutyl rubber, polystyrene elastomers, polyethyleneelastomers, polyurethane elastomers, polyurea elastomers,metallocene-catalyzed elastomers and plastomers, copolymers ofisobutylene and p-alkylstyrene, halogenated copolymers of isobutyleneand p-alkylstyrene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber,acrylonitrile chlorinated isoprene rubber, and blends of two or morethereof. Preferably, the outer core layer is formed from a polybutadienerubber composition.

The thermoset rubber composition may be cured using conventional curingprocesses. Suitable curing processes include, for example,peroxide-curing, sulfur-curing, high-energy radiation, and combinationsthereof. Preferably, the rubber composition contains a free-radicalinitiator selected from organic peroxides, high energy radiation sourcescapable of generating free-radicals, and combinations thereof. In onepreferred version, the rubber composition is peroxide-cured. Suitableorganic peroxides include, but are not limited to, dicumyl peroxide;n-butyl-4,4-di(t-butylperoxy) valerate;1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane;2,5-dimethyl-2,5-di(t-butylperoxy) hexane; di-t-butyl peroxide;di-t-amyl peroxide; t-butyl peroxide; t-butyl cumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3;di(2-t-butyl-peroxyisopropyl)benzene; dilauroyl peroxide; dibenzoylperoxide; t-butyl hydroperoxide; and combinations thereof. In aparticular embodiment, the free radical initiator is dicumyl peroxide,including, but not limited to Perkadox® BC, commercially available fromAkzo Nobel. Peroxide free-radical initiators are generally present inthe rubber composition in an amount of at least 0.05 parts by weight per100 parts of the total rubber, or an amount within the range having alower limit of 0.05 parts or 0.1 parts or 1 part or 1.25 parts or 1.5parts or 2.5 parts or 5 parts by weight per 100 parts of the totalrubbers, and an upper limit of 2.5 parts or 3 parts or 5 parts or 6parts or 10 parts or 15 parts by weight per 100 parts of the totalrubber. Concentrations are in parts per hundred (phr) unless otherwiseindicated. As used herein, the term, “parts per hundred,” also known as“phr” or “pph” is defined as the number of parts by weight of aparticular component present in a mixture, relative to 100 parts byweight of the polymer component. Mathematically, this can be expressedas the weight of an ingredient divided by the total weight of thepolymer, multiplied by a factor of 100.

The rubber compositions may further include a reactive cross-linkingco-agent. Suitable co-agents include, but are not limited to, metalsalts of unsaturated carboxylic acids having from 3 to 8 carbon atoms;unsaturated vinyl compounds and polyfunctional monomers (e.g.,trimethylolpropane trimethacrylate); phenylene bismaleimide; andcombinations thereof. Particular examples of suitable metal saltsinclude, but are not limited to, one or more metal salts of acrylates,diacrylates, methacrylates, and dimethacrylates, wherein the metal isselected from magnesium, calcium, zinc, aluminum, lithium, and nickel.In a particular embodiment, the co-agent is selected from zinc salts ofacrylates, diacrylates, methacrylates, and dimethacrylates. In anotherparticular embodiment, the agent is zinc diacrylate (ZDA). When theco-agent is zinc diacrylate and/or zinc dimethacrylate, the co-agent istypically included in the rubber composition in an amount within therange having a lower limit of 1 or 5 or 10 or 15 or 19 or 20 parts byweight per 100 parts of the total rubber, and an upper limit of 24 or 25or 30 or 35 or 40 or 45 or 50 or 60 parts by weight per 100 parts of thebase rubber.

Radical scavengers such as a halogenated organosulfur, organicdisulfide, or inorganic disulfide compounds may be added to the rubbercomposition. These compounds also may function as “soft and fastagents.” As used herein, “soft and fast agent” means any compound or ablend thereof that is capable of making a core: 1) softer (having alower compression) at a constant “coefficient of restitution” (COR);and/or 2) faster (having a higher COR at equal compression), whencompared to a core equivalently prepared without a soft and fast agent.Preferred halogenated organosulfur compounds include, but are notlimited to, pentachlorothiophenol (PCTP) and salts of PCTP such as zincpentachlorothiophenol (ZnPCTP). Using PCTP and ZnPCTP in golf ball innercores helps produce softer and faster inner cores. The PCTP and ZnPCTPcompounds help increase the resiliency and the coefficient ofrestitution of the core. In a particular embodiment, the soft and fastagent is selected from ZnPCTP, PCTP, ditolyl disulfide, diphenyldisulfide, dixylyl disulfide, 2-nitroresorcinol, and combinationsthereof.

The rubber composition also may include filler(s) such as materialsselected from carbon black, nanoclays (e.g., Cloisite® and Nanofil®nanoclays, commercially available from Southern Clay Products, Inc., andNanomax® and Nanomer® nanoclays, commercially available from Nanocor,Inc.), talc (e.g., Luzenac HAR® high aspect ratio talcs, commerciallyavailable from Luzenac America, Inc.), glass (e.g., glass flake, milledglass, and microglass), mica and mica-based pigments (e.g., Iriodin®pearl luster pigments, commercially available from The Merck Group), andcombinations thereof. Metal fillers such as, for example, particulate;powders; flakes; and fibers of copper, steel, brass, tungsten, titanium,aluminum, magnesium, molybdenum, cobalt, nickel, iron, lead, tin, zinc,barium, bismuth, bronze, silver, gold, and platinum, and alloys andcombinations thereof also may be added to the rubber composition toadjust the specific gravity of the composition as needed.

In addition, the rubber compositions may include antioxidants to preventthe breakdown of the elastomers. Also, processing aids such as highmolecular weight organic acids and salts thereof may be added to thecomposition. Suitable organic acids are aliphatic organic acids,aromatic organic acids, saturated mono-functional organic acids,unsaturated monofunctional organic acids, multi-unsaturatedmono-functional organic acids, and dimerized derivatives thereof.Particular examples of suitable organic acids include, but are notlimited to, caproic acid, caprylic acid, capric acid, lauric acid,stearic acid, behenic acid, erucic acid, oleic acid, linoleic acid,myristic acid, benzoic acid, palmitic acid, phenylacetic acid,naphthalenoic acid, and dimerized derivatives thereof. The organic acidsare aliphatic, mono-functional (saturated, unsaturated, ormulti-unsaturated) organic acids. Salts of these organic acids may alsobe employed. The salts of organic acids include the salts of barium,lithium, sodium, zinc, bismuth, chromium, cobalt, copper, potassium,strontium, titanium, tungsten, magnesium, cesium, iron, nickel, silver,aluminum, tin, or calcium, salts of fatty acids, particularly stearic,behenic, erucic, oleic, linoelic or dimerized derivatives thereof. It ispreferred that the organic acids and salts of the present invention berelatively non-migratory (they do not bloom to the surface of thepolymer under ambient temperatures) and non-volatile (they do notvolatilize at temperatures required for melt-blending.) Otheringredients such as accelerators (for example, tetra methylthiuram),processing aids, dyes and pigments, wetting agents, surfactants,plasticizers, coloring agents, fluorescent agents, chemical blowing andfoaming agents, defoaming agents, stabilizers, softening agents, impactmodifiers, antiozonants, as well as other additives known in the art maybe added to the rubber composition.

Examples of commercially-available polybutadiene rubbers that can beused in accordance with this invention, include, but are not limited to,BR 01 and BR 1220, available from BST Elastomers of Bangkok, Thailand;SE BR 1220LA and SE BR1203, available from DOW Chemical Co of Midland,Mich.; BUDENE 1207, 1207s, 1208, and 1280 available from Goodyear, Incof Akron, Ohio; BR 01, 51 and 730, available from Japan Synthetic Rubber(JSR) of Tokyo, Japan; BUNA CB 21, CB 22, CB 23, CB 24, CB 25, CB 29MES, CB 60, CB Nd 60, CB 55 NF, CB 70 B, CB KA 8967, and CB 1221,available from Lanxess Corp. of Pittsburgh. Pa.; BR1208, available fromLG Chemical of Seoul, South Korea; UBEPOL BR130B, BR150, BR150B, BR150L,BR230, BR360L, BR710, and VCR617, available from UBE Industries, Ltd. ofTokyo, Japan; EUROPRENE NEOCIS BR 60, INTENE 60 AF and P30AF, andEUROPRENE BR HV80, available from Polimeri Europa of Rome, Italy; AFDENE50 and NEODENE BR40, BR45, BR50 and BR60, available from Karbochem (PTY)Ltd. of Bruma, South Africa; KBR 01, NdBr 40, NdBR-45, NdBr 60, KBR710S, KBR 710H, and KBR 750, available from Kumho Petrochemical Co.,Ltd. Of Seoul, South Korea; DIENE 55NF, 70AC, and 320 AC, available fromFirestone Polymers of Akron, Ohio; and PBR-Nd Group II and Group III,available from Nizhnekamskneftekhim, Inc. of Nizhnekamsk, TartarstanRepublic.

The polybutadiene rubber is used in an amount of at least about 5% byweight based on total weight of composition and is generally present inan amount of about 5% to about 100%, or an amount within a range havinga lower limit of 5% or 10% or 20% or 30% or 40% or 50% and an upperlimit of 55% or 60% or 70% or 80% or 90% or 95% or 100%. Preferably, theconcentration of polybutadiene rubber is about 40 to about 95 weightpercent. If desirable, lesser amounts of other thermoset materials maybe incorporated into the base rubber. Such materials include the rubbersdiscussed above, for example, cis-polyisoprene, trans-polyisoprene,balata, polychloroprene, polynorbornene, polyoctenamer, polypentenamer,butyl rubber, EPR, EPDM, styrene-butadiene, and the like.

Core Structure

As discussed above, the core preferably has a multi-layered structurecomprising an inner core, intermediate core layer, and outer core layer.In FIG. 3, a partial cut-away view of one version of the core (17) ofthis invention is shown. The core (17) includes an inner core (18)comprising a foamed composition; an intermediate core layer (20)comprising a thermoplastic composition; and an outer core layer (22)comprising a thermoset composition. As shown in FIG. 3, the intermediatecore layer (20) is disposed about the inner core (18), and the outercore layer (22) surrounds the intermediate core layer. The hardness ofthe core sub-assembly (inner core, intermediate core layer, and outercore layer) is an important property. In general, cores with relativelyhigh hardness values have higher compression and tend to have gooddurability and resiliency. However, some high compression balls arestiff and this may have a detrimental effect on shot control andplacement. Thus, the optimum balance of hardness in the coresub-assembly needs to be attained.

In one preferred golf ball, the inner core (center) has a “positive”hardness gradient (that is, the outer surface of the inner core isharder than its geometric center); the intermediate core layer has a“positive” hardness gradient (that is, the outer surface of theintermediate core layer is harder than the inner surface of theintermediate core layer); and the outer core layer has a “positive”hardness gradient (that is, the outer surface of the outer core layer isharder than the inner surface of the outer core layer.) In such caseswhere the inner core; intermediate; and outer core layer each has a“positive” hardness gradient, the outer surface hardness of the outercore layer is preferably greater than the hardness of the geometriccenter of the inner core. In one preferred version, the positivehardness gradient of the inner core is in the range of about 2 to about40 Shore C units and even more preferably about 10 to about 25 Shore Cunits; while the positive hardness gradient of the intermediate core isin the range of about 1 to about 5 Shore C; and the positive hardnessgradient of the outer core is in the range of about 2 to about 20 ShoreC and even more preferably about 3 to about 10 Shore C.

In an alternative version, the inner core may have a positive hardnessgradient; the intermediate core layer may have a “zero” hardnessgradient (that is, the hardness values of the outer surface of theintermediate core layer and the inner surface of the intermediate corelayer are substantially the same) or a “negative” hardness gradient(that is, the outer surface of the intermediate core layer is softerthan the inner surface of the intermediate core layer); and the outercore layer may have a “zero” hardness gradient (that is, the hardnessvalues of the outer surface of the outer core layer and the innersurface of the outer core layer are substantially the same) or a“negative” hardness gradient (that is, the outer surface of the outercore layer is softer than the inner surface of the outer core layer.)For example, in one version, the inner core has a positive hardnessgradient; the intermediate core layer has a zero hardness gradient; andthe outer core layer has a negative hardness gradient in the range ofabout 2 to about 25 Shore C. Alternatively, the inner core may have apositive hardness gradient; the intermediate core layer may have a zeroor negative hardness gradient; and the outer core layer may have apositive hardness gradient. Still yet, in another preferred embodiment,both the inner core and intermediate core layers have positive hardnessgradients (more preferably within the range of about 2 to about 40 ShoreC), while the outer core layer has a zero or negative hardness gradient.

In another version, the inner core (center) has a zero or negativehardness gradient, while the intermediate core layer has a positivehardness gradient, and the outer core has a zero or negative hardnessgradient. In yet another version, both the inner core and intermediatecore layers have a zero or negative hardness gradient, while the outercore layer has a positive hardness gradient. Alternatively, in a furtherversion, the inner core has a zero or negative hardness gradient, whileboth the intermediate and outer core layers have positive hardnessgradients. Finally, in still yet another version, the inner core,intermediate core, and outer core layer each has a zero or negativehardness gradient.

In general, hardness gradients are further described in Bulpett et al.,U.S. Pat. Nos. 7,537,529 and 7,410,429, the disclosures of which arehereby incorporated by reference. Methods for measuring the hardness ofthe inner core, intermediate core, and outer core layers along withother layers in the golf ball and determining the hardness gradients ofthe various layers are described in further detail below. The corelayers have positive, negative, or zero hardness gradients defined byhardness measurements made at the outer surface of the inner core (orouter surface of the intermediate or outer core layer) and radiallyinward towards the center of the inner core (or inner surface of theintermediate or outer core layer). These measurements are made typicallyat 2-mm increments as described in the test methods below. In general,the hardness gradient is determined by subtracting the hardness value atthe innermost portion of the component being measured (for example, thecenter of the inner core or inner surface of the intermediate or outercore layer) from the hardness value at the outer surface of thecomponent being measured (for example, the outer surface of the innercore or outer surface of the intermediate or outer core layer).

Positive Hardness Gradient.

For example, if the hardness value of the outer surface of the innercore is greater than the hardness value of the inner core's geometriccenter (that is, the inner core has a surface harder than its geometriccenter), the hardness gradient will be deemed “positive” (a largernumber minus a smaller number equals a positive number.) For example, ifthe outer surface of the inner core has a hardness of 67 Shore C and thegeometric center of the inner core has a hardness of 60 Shore C, thenthe inner core has a positive hardness gradient of 7. Likewise, if theouter surface of the intermediate (or outer) core layer has a greaterhardness value than the inner surface of the intermediate (or outer)core layer respectively, the given intermediate (and/or outer) corelayer will be considered to have a positive hardness gradient.

Negative Hardness Gradient.

On the other hand, if the hardness value of the outer surface of theinner core is less than the hardness value of the inner core's geometriccenter (that is, the inner core has a surface softer than its geometriccenter), the hardness gradient will be deemed “negative.” For example,if the outer surface of the inner core has a hardness of 68 Shore C andthe geometric center of the inner core has a hardness of 70 Shore C,then the inner core has a negative hardness gradient of 2. Likewise, ifthe outer surface of the intermediate (or outer) core layer has a lesserhardness value than the inner surface of the intermediate (or outer)core layer, the given intermediate (and/or outer) core layer will beconsidered to have a negative hardness gradient.

Zero Hardness Gradient.

In another example, if the hardness value of the outer surface of theinner core is substantially the same as the hardness value of the innercore's geometric center (that is, the surface of the inner core hasabout the same hardness as the geometric center), the hardness gradientwill be deemed “zero.” For example, if the outer surface of the innercore and the geometric center of the inner core each has a hardness of65 Shore C, then the inner core has a zero hardness gradient. Likewise,if the outer surface of the outer core layer has a hardness valueapproximately the same as the inner surface of the outer core layer, theouter core layer will be considered to have a zero hardness gradient.Also, if the outer surface of the intermediate core layer has a hardnessvalue approximately the same as the inner surface of the intermediatecore layer, the intermediate core layer will be considered to have azero hardness gradient.

More particularly, the term, “positive hardness gradient” as used hereinmeans a hardness gradient of positive 3 Shore C or greater, preferably 7Shore C or greater, more preferably 10 Shore C, and even more preferably20 Shore C or greater. The term, “zero hardness gradient” as used hereinmeans a hardness gradient of less than 3 Shore C, preferably less than 1Shore C and may have a value of zero or negative 1 to negative 10 ShoreC. The term, “negative hardness gradient” as used herein means ahardness value of less than zero, for example, negative 3, negative 5,negative 7, negative 10, negative 15, or negative 20 or negative 25. Theterms, “zero hardness gradient” and “negative hardness gradient” may beused herein interchangeably to refer to hardness gradients of negative 1to negative 10.

The inner core preferably has a geometric center hardness(H_(inner core center)) of about 5 Shore D or greater. For example, the(H_(inner core center)) may be in the range of about 5 to about 88 ShoreD and more particularly within a range having a lower limit of about 5or 10 or 18 or 20 or 26 or 30 or 34 or 36 or 38 or 42 or 48 of 50 or 52Shore D and an upper limit of about 54 or 56 or 58 or 60 or 62 or 64 or68 or 70 or 74 or 76 or 80 or 82 or 84 or 88 Shore D. In anotherexample, the center hardness of the inner core (H_(inner core center)),as measured in Shore C units, is preferably about 10 Shore C or greater;for example, the H_(inner core center) may have a lower limit of about10 or 14 or 16 or 22 or 24 or 28 or 31 or 34 or 37 or 40 or 44 or 52 or58 Shore C and an upper limit of about or 60 or 62 or 65 or 68 or 71 or74 or 76 or 78 or 79 or 80 or 84 or 90 Shore C. Concerning the outersurface hardness of the inner core (H_(inner core surface)), thishardness is preferably about 15 Shore D or greater; for example, theH_(inner core surface) may fall within a range having a lower limit ofabout 15 or 18 or 20 or 23 or 26 or 30 or 34 or 36 or 38 or 42 or 48 of50 or 52 Shore D and an upper limit of about 54 or 56 or 58 or 60 or 62or 70 or 72 or 75 or 78 or 80 or 82 or 84 or 86 or 90 Shore D. In oneversion, the outer surface hardness of the inner core(H_(inner core surface)), as measured in Shore C units, has a lowerlimit of about 20 or 24 or 27 or 28 or 30 or 32 or 34 or 38 or 44 or 52or 58 or 60 or 70 or 74 Shore C and an upper limit of about 76 or 78 or80 or 84 or 86 or 88 or 90 or 92 Shore C.

Meanwhile, the intermediate core layer preferably has an outer surfacehardness (H_(outer surface of IC)) of about 30 Shore D or greater, andmore preferably within a range having a lower limit of about 30 or 35 or40 or 42 or 44 or 46 or 48 or 50 or 52 or 54 or 56 or 58 and an upperlimit of about 60 or 62 or 64 or 70 or 74 or 78 or 80 or 82 or 85 or 87or 88 or 90 Shore D. The outer surface hardness of the intermediate corelayer (H_(outer surface of IC)), as measured in Shore C units,preferably has a lower limit of about 63 or 65 or 67 or 70 or 73 or 75or 76 or 78 Shore C, and an upper limit of about 78 or 80 or 85 or 87 or89 or 90 or 92 or 95 Shore C. While, the inner surface hardness of theintermediate core (H_(inner surface of the IC)) preferably is about 25Shore D or greater and more preferably is within a range having a lowerlimit of about 26 or 30 or 34 or 36 or 38 or 42 or 48 of 50 or 52 ShoreD and an upper limit of about 54 or 56 or 58 or 60 or 62 Shore D. Asmeasured in Shore C units, the inner surface hardness of theintermediate core (H_(inner surface of the IC)) preferably has a lowerlimit of about 38 or 44 or 52 or 58 or 60 or 70 or 74 Shore C and anupper limit of about 76 or 78 or 80 or 84 or 86 or 88 or 90 or 92 ShoreC.

On the other hand, the outer core layer preferably has an outer surfacehardness (H_(outer surface of OC)) of about 40 Shore D or greater, andmore preferably within a range having a lower limit of about 40 or 42 or44 or 46 or 48 or 50 or 52 and an upper limit of about 54 or 56 or 58 or60 or 62 or 64 or 70 or 74 or 78 or 80 or 82 or 85 or 87 or 88 or 90Shore D. The outer surface hardness of the outer core layer(H_(outer surface of OC)), as measured in Shore C units, preferably hasa lower limit of about 40 or 42 or 45 or 48 or 50 or 54 or 58 or 60 or63 or 65 or 67 or 70 or 73 or 76 Shore C, and an upper limit of about 78or 80 or 84 or 85 or 87 or 89 or 90 or 92 or 95 Shore C. And, the innersurface of the outer core layer (H_(inner surface of OC)) preferably hasa hardness of about 40 Shore D or greater, and more preferably within arange having a lower limit of about 40 or 42 or 44 or 46 or 48 or 50 or52 and an upper limit of about 54 or 56 or 58 or 60 or 62 or 64 or 70 or74 or 78 or 80 or 82 or 85 or 87 or 88 or 90 Shore D. The inner surfacehardness of the outer core layer (H_(inner surface of OC)), as measuredin Shore C units, preferably has a lower limit of about 40 or 44 or 45or 47 or 50 or 52 or 54 or 55 or 58 or 60 or 63 or 65 or 67 or 70 or 73or 76 Shore C, and an upper limit of about 78 or 80 or 85 or 87 or 89 or90 or 92 or 95 Shore C.

In one preferred embodiment, the outer surface hardness of theintermediate core layer (H_(outer surface of IC)), is less than theouter surface hardness (H_(inner core surface)) of the inner core by atleast 3 Shore C units and more preferably by at least 5 Shore C.

In a second preferred embodiment, the outer surface hardness of theintermediate core layer (H_(outer surface of IC)), is greater than theouter surface hardness (H_(inner core surface)) of the inner core by atleast 3 Shore C units and more preferably by at least 5 Shore C.

The inner core preferably has a diameter in the range of about 0.100 toabout 1.100 inches, and the volume of the inner core is preferably inthe range of about 0.01 to about 11.4 cc. For example, the inner coremay have a diameter within a range of about 0.100 to about 0.500 inches.In another example, the inner core may have a diameter within a range ofabout 0.300 to about 0.800 inches. More particularly, the inner corepreferably has a diameter size with a lower limit of about 0.10 or 0.12or 0.15 or 0.25 or 0.30 or 0.35 or 0.45 or 0.55 inches and an upperlimit of about 0.60 or 0.65 or 0.70 or 0.80 or 0.90 or 1.00 or 1.10inches. Concerning the volume, the inner core may have a volume with alower limit of 0.01 or 0.5 or 1.0 or 1.07 or 1.5 or 2.25 or 3.0 or 3.5or 4.0 or 5.0 or 5.5 or 6.5 cc and an upper limit of 7.0 or 8.0 or 8.25or 8.5 or 9.0 or 9.5 or 10.0 or 11.25 or 11.4 cc.

Meanwhile, the intermediate core layer preferably has a thickness in therange of about 0.050 to about 0.400 inches. More particularly, thethickness of the intermediate core layer preferably has a lower limit ofabout 0.050 or 0.060 or 0.070 or 0.075 or 0.080 inches and an upperlimit of about 0.090 or 0.100 or 0.130 or 0.200 or 0.250 or 0.300 or0.400 inches. For example, the intermediate core layer may have a volumewith a lower limit of 0.06 or 0.1 or 0.5 or 1.25 or 2.0 or 3.0 or 3.4 or4.0 or 4.25 or 5.0 or 5.5 or 6.0 or 6.24 or 7.0 or 8.0 cc and an upperlimit of 9.0 or 10.0 or 10.5 or 11.0 or 12.0 or 12.25 or 13.0 or 14.0 or14.5 or 15.0 or 16.0 or 16.5 or 17.0 or 17.8 cc.

As far as the outer core layer is concerned, it preferably has athickness in the range of about 0.200 to about 0.750 inches and thevolume of the outer core layer preferably is in the range of about 1.78to about 42.04 cc. For example, the lower limit of thickness may beabout 0.200 or 0.250 or 0.300 or 0.340 or 0.400 and the upper limit maybe about 0.500 or 0.550 or 0.600 or 0.650 or 0.700 or 0.750 inches. Forexample, the outer core layer may have a volume with a lower limit of1.78 or 4.00 or 6.30 or 8.00 or 10.60 or 12.00 or 16.20 or 20.10 cc andan upper limit of 22.00 or 24.30 or 26.40 or 30.00 or 34.10 or 38.20 or40.00 or 42.04 cc.

Multi-layered core structures containing layers with various thicknessand volume levels may be made in accordance with this invention. Forexample, in one version, the total diameter of the inner core andintermediate core is 0.2 inches and the total volume of the inner andintermediate core is 0.07 cc. More particularly, in this example, thevolume of the intermediate core layer is 0.06 cc and the volume of theinner core is 0.01 cc. In one preferred embodiment, the volume of theouter core layer is greater than the volume of each of the inner andintermediate core layers. In another preferred embodiment, the volume ofthe intermediate core layer is greater than the volume of the inner corelayer. Thus, some core structure examples include an outer core layerhaving a relatively large volume; an intermediate core layer having arelatively mid-size volume, and an inner core having a relatively smallvolume. That is, the volume of the outer core layer is greater than thevolume of the intermediate core layer; and the volume of theintermediate core layer is greater than the volume of the inner core. Inone particular version, the volume of the outer core layer is greaterthan the volume of the intermediate core layer; and the volume of theintermediate core layer is greater than the volume of the inner core.Other examples of core structures containing layers of varying thicknessand volume are described below in Tables 1 and 2.

TABLE 1 Core Dimensions and Volumes Dimensions of Total Total VolumeVolume Core Layers Diameter Volume of MC of IC MC* of 0.05″ 0.2″ 0.07 cc0.06 cc 0.01 cc thickness and IC** of 0.1″ diameter. MC of 0.05″ 1.2″14.8 cc  3.4 cc 11.4 cc thickness and IC of 1.1″ diameter. MC of 0.40″0.9″ 6.25 cc 6.24 cc 0.01 cc thickness and IC of 0.1″ diameter. MC of0.40″ 1.3″ 18.9 cc 17.8 cc 1.07 cc thickness and IC of 0.5″ diameter.*MC—intermediate core layer **IC—inner core layer

TABLE 2 Core Dimensions and Volumes Dimensions of Total Total VolumeVolume Core Layers Diameter Volume of OC of MC OC* of 0.2″ 0.6″ 1.85 cc1.78 cc 0.06 cc thickness; MC** of 0.05″ thickness; and IC*** of 0.1″diameter. OC of 0.2″ 1.6″ 35.1 cc 20.3 cc  3.4 cc thickness; MC of 0.05″thickness and IC of 1.1″ diameter. OC of 0.75″ 1.7″ 42.1 cc 42.04 cc 0.06 cc thickness; MC of 0.05″ thickness and IC of 0.1″ diameter.*OC—outer core layer **MC—intermediate core layer ***IC—inner core layer

As discussed above, the inner core is preferably formed from a foamedthermoplastic or thermoset composition and more preferably foamedpolyurethanes. Likewise, the intermediate and outer core layers may beformed from thermoset or thermoplastic materials. Preferably, theintermediate core layer is formed from a non-foamed thermoplasticcomposition such as ethylene acid copolymer ionomers; and the outer corelayer is formed from a non-foamed thermoset composition such aspolybutadiene rubber.

In one preferred embodiment, the inner core has a specific gravity inthe range of about 0.25 to about 1.25 g/cc. Also, as discussed above,the specific gravity of the inner core may vary at different points ofthe inner core structure. That is, there may be a specific gravitygradient in the inner core. For example, in one preferred version, thegeometric center of the inner core has a density in the range of about0.25 to about 0.75 g/cc; while the outer skin of the inner core has adensity in the range of about 0.75 to about 1.50 g/cc.

Meanwhile, the intermediate and outer core layers preferably haverelatively high specific gravities. Thus, the specific gravity of theinner core layer (SG_(inner)) is preferably less than the specificgravity of the intermediate core layer (SG_(intermediate)) and outercore layer (SG_(outer)). By the term, “specific gravity of theintermediate core layer” (“SG_(intermediate)”), it is generally meantthe specific gravity of the intermediate core layer as measured at anypoint of the intermediate core layer. By the term, “specific gravity ofthe outer core layer” (“SG_(outer)”), it is generally meant the specificgravity of the outer core layer as measured at any point of the outercore layer as discussed above with respect to the inner core. Thespecific gravity values at different points in the intermediate andouter core layers may vary. That is, there may be specific gravitygradients in the intermediate and outer core layers similar to the innercore. For example, the intermediate and outer core layers each may havea specific gravity within a range having a lower limit of about 0.50 or0.60 or 0.70 or 0.75 or 0.85 or 0.95 or 1.00 or 1.10 or 1.25 or 1.30 or1.36 or 1.40 or 1.42 or 1.48 or 1.50 or 1.60 or 1.66 or 1.75 or 2.00 andan upper limit of 2.50 or 2.60 or 2.80 or 2.90 or 3.00 or 3.10 or 3.25or 3.50 or 3.60 or 3.80 or 4.00, 4.25 or 5.00 or 5.10 or 5.20 or 5.30 or5.40 or 6.00 or 6.20 or 6.25 or 6.30 or 6.40 or 6.50 or 7.00 or 7.10 or7.25 or 7.50 or 7.60 or 7.65 or 7.80 or 8.00 or 8.20 or 8.50 or 9.00 or9.75 or 10.00 g/cc.

In general, the specific gravities of the respective pieces of an objectaffect the Moment of Inertia (MOI) of the object. The Moment of Inertiaof a ball (or other object) about a given axis generally refers to howdifficult it is to change the ball's angular motion about that axis. Ifthe ball's mass is concentrated towards the center (the center piece(for example, inner core) has a higher specific gravity than the outerpiece (for example, outer core layers), less force is required to changeits rotational rate, and the ball has a relatively low Moment ofInertia. In such balls, most of the mass is located close to the ball'saxis of rotation and less force is needed to generate spin. Thus, theball has a generally high spin rate as the ball leaves the club's faceafter making impact. Conversely, if the ball's mass is concentratedtowards the outer surface (the outer piece (for example, outer corelayers) has a higher specific gravity than the center piece (forexample, inner core), more force is required to change its rotationalrate, and the ball has a relatively high Moment of Inertia. That is, insuch balls, most of the mass is located away from the ball's axis ofrotation and more force is needed to generate spin. Such balls have agenerally low spin rate as the ball leaves the club's face after makingimpact.

More particularly, as described in Sullivan, U.S. Pat. No. 6,494,795 andLadd et al., U.S. Pat. No. 7,651,415, the formula for the Moment ofInertia for a sphere through any diameter is given in the CRC StandardMathematical Tables, 24th Edition, 1976 at 20 (hereinafter CRCreference). The term, “specific gravity” as used herein, has itsordinary and customary meaning, that is, the ratio of the density of asubstance to the density of water at 4° C., and the density of water atthis temperature is 1 g/cm³.

In one embodiment, the golf balls of this invention are relatively lowspin and long distance. That is, the foam core construction, asdescribed above, wherein the inner core is made of a foamed compositionhelps provide a relatively low spin ball having good resiliency. Theinner foam cores of this invention preferably have a Coefficient ofRestitution (COR) of about 0.300 or greater; more preferably about 0.400or greater, and even more preferably about 0.450 or greater. Theresulting balls containing the multi-layered core constructions of thisinvention and cover of at least one layer preferably have a COR of about0.700 or greater, more preferably about 0.730 or greater; and even morepreferably about 0.750 to 0.810 or greater. The inner foam corespreferably have a Soft Center Deflection Index (“SCDI”) compression, asdescribed in the Test Methods below, in the range of about 50 to about190, and more preferably in the range of about 60 to about 170.

The USGA has established a maximum weight of 45.93 g (1.62 ounces) forgolf balls. For play outside of USGA rules, the golf balls can beheavier. In one preferred embodiment, the weight of the multi-layeredcore is in the range of about 28 to about 38 grams. Also, golf ballsmade in accordance with this invention can be of any size, although theUSGA requires that golf balls used in competition have a diameter of atleast 1.68 inches. For play outside of United States Golf Association(USGA) rules, the golf balls can be of a smaller size. Normally, golfballs are manufactured in accordance with USGA requirements and have adiameter in the range of about 1.68 to about 1.80 inches. As discussedfurther below, the golf ball contains a cover which may be multi-layeredand in addition may contain intermediate (casing) layers, and thethickness levels of these layers also must be considered. Thus, ingeneral, the multi-layer core structure normally has an overall diameterwithin a range having a lower limit of about 1.00 or 1.20 or 1.30 or1.40 inches and an upper limit of about 1.58 or 1.60 or 1.62 or 1.66inches, and more preferably in the range of about 1.3 to 1.65 inches. Inone embodiment, the diameter of the core sub-assembly is in the range ofabout 1.45 to about 1.62 inches.

Cover Structure

The golf ball sub-assemblies of this invention may be enclosed with oneor more cover layers. The golf ball sub-assembly may comprise themulti-layered core structure as discussed above. In other versions, thegolf ball sub-assembly includes the core structure and one or morecasing (mantle) layers disposed about the core. In one particularlypreferred version, the golf ball includes a multi-layered covercomprising inner and outer cover layers. The inner cover layer ispreferably formed from a composition comprising an ionomer or a blend oftwo or more ionomers that helps impart hardness to the ball. In aparticular embodiment, the inner cover layer is formed from acomposition comprising a high acid ionomer. A particularly suitable highacid ionomer is Surlyn 8150® (DuPont). Surlyn 8150® is a copolymer ofethylene and methacrylic acid, having an acid content of 19 wt %, whichis 45% neutralized with sodium. In another particular embodiment, theinner cover layer is formed from a composition comprising a high acidionomer and a maleic anhydride-grafted non-ionomeric polymer. Aparticularly suitable maleic anhydride-grafted polymer is Fusabond 525D®(DuPont). Fusabond 525D® is a maleic anhydride-grafted,metallocene-catalyzed ethylene-butene copolymer having about 0.9 wt %maleic anhydride grafted onto the copolymer. A particularly preferredblend of high acid ionomer and maleic anhydride-grafted polymer is an 84wt %/16 wt % blend of Surlyn 8150® and Fusabond 525D®. Blends of highacid ionomers with maleic anhydride-grafted polymers are furtherdisclosed, for example, in U.S. Pat. Nos. 6,992,135 and 6,677,401, theentire disclosures of which are hereby incorporated herein by reference.

The inner cover layer also may be formed from a composition comprising a50/45/5 blend of Surlyn® 8940/Surlyn® 9650/Nucrel® 960, and, in aparticularly preferred embodiment, the composition has a materialhardness of from 80 to 85 Shore C. In yet another version, the innercover layer is formed from a composition comprising a 50/25/25 blend ofSurlyn® 8940/Surlyn® 9650/Surlyn® 9910, preferably having a materialhardness of about 90 Shore C. The inner cover layer also may be formedfrom a composition comprising a 50/50 blend of Surlyn® 8940/Surlyn®9650, preferably having a material hardness of about 86 Shore C. Acomposition comprising a 50/50 blend of Surlyn® 8940 and Surlyn® 7940also may be used. Surlyn® 8940 is an E/MAA copolymer in which the MAAacid groups have been partially neutralized with sodium ions. Surlyn®9650 and Surlyn® 9910 are two different grades of E/MAA copolymer inwhich the MAA acid groups have been partially neutralized with zincions. Nucrel® 960 is an E/MAA copolymer resin nominally made with 15 wt% methacrylic acid.

A wide variety of materials may be used for forming the outer coverincluding, for example, polyurethanes; polyureas; copolymers, blends andhybrids of polyurethane and polyurea; olefin-based copolymer ionomerresins (for example, Surlyn® ionomer resins and DuPont HPF® 1000 andHPF® 2000, commercially available from DuPont; Iotek® ionomers,commercially available from ExxonMobil Chemical Company; Amplify® IOionomers of ethylene acrylic acid copolymers, commercially availablefrom The Dow Chemical Company; and Clarix® ionomer resins, commerciallyavailable from A. Schulman Inc.); polyethylene, including, for example,low density polyethylene, linear low density polyethylene, and highdensity polyethylene; polypropylene; rubber-toughened olefin polymers;acid copolymers, for example, poly(meth)acrylic acid, which do notbecome part of an ionomeric copolymer; plastomers; flexomers;styrene/butadiene/styrene block copolymers;styrene/ethylene-butylene/styrene block copolymers; dynamicallyvulcanized elastomers; copolymers of ethylene and vinyl acetates;copolymers of ethylene and methyl acrylates; polyvinyl chloride resins;polyamides, poly(amide-ester) elastomers, and graft copolymers ofionomer and polyamide including, for example, Pebax® thermoplasticpolyether block amides, commercially available from Arkema Inc;cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, commercially available fromDuPont or RiteFlex®, commercially available from Ticona EngineeringPolymers; polyurethane-based thermoplastic elastomers, such asElastollan®, commercially available from BASF; synthetic or naturalvulcanized rubber; and combinations thereof. Castable polyurethanes,polyureas, and hybrids of polyurethanes-polyureas are particularlydesirable because these materials can be used to make a golf ball havinghigh resiliency and a soft feel. By the term, “hybrids of polyurethaneand polyurea,” it is meant to include copolymers and blends thereof.

Polyurethanes, polyureas, and blends, copolymers, and hybrids ofpolyurethane/polyurea are also particularly suitable for forming coverlayers. When used as cover layer materials, polyurethanes and polyureascan be thermoset or thermoplastic. Thermoset materials can be formedinto golf ball layers by conventional casting or reaction injectionmolding techniques. Thermoplastic materials can be formed into golf balllayers by conventional compression or injection molding techniques.

The compositions used to make the casing (mantle) and cover layers maycontain a wide variety of fillers and additives to impart specificproperties to the ball. For example, relatively heavy-weight andlight-weight metal fillers such as, particulate; powders; flakes; andfibers of copper, steel, brass, tungsten, titanium, aluminum, magnesium,molybdenum, cobalt, nickel, iron, lead, tin, zinc, barium, bismuth,bronze, silver, gold, and platinum, and alloys and combinations thereofmay be used to adjust the specific gravity of the ball. Other additivesand fillers include, but are not limited to, optical brighteners,coloring agents, fluorescent agents, whitening agents, UV absorbers,light stabilizers, surfactants, processing aids, antioxidants,stabilizers, softening agents, fragrance components, plasticizers,impact modifiers, titanium dioxide, clay, mica, talc, glass flakes,milled glass, and mixtures thereof.

The inner cover layer preferably has a material hardness within a rangehaving a lower limit of 70 or 75 or 80 or 82 Shore C and an upper limitof 85 or 86 or 90 or 92 Shore C. The thickness of the intermediate layeris preferably within a range having a lower limit of 0.010 or 0.015 or0.020 or 0.030 inches and an upper limit of 0.035 or 0.045 or 0.080 or0.120 inches. The outer cover layer preferably has a material hardnessof 85 Shore C or less. The thickness of the outer cover layer ispreferably within a range having a lower limit of 0.010 or 0.015 or0.025 inches and an upper limit of 0.035 or 0.040 or 0.055 or 0.080inches. Methods for measuring hardness of the layers in the golf ballare described in further detail below.

A single cover or, preferably, an inner cover layer is formed around theouter core layer. When an inner cover layer is present, an outer coverlayer is formed over the inner cover layer. Most preferably, the innercover is formed from an ionomeric material and the outer cover layer isformed from a polyurethane material, and the outer cover layer has ahardness that is less than that of the inner cover layer. Preferably,the inner cover has a hardness of greater than about 60 Shore D and theouter cover layer has a hardness of less than about 60 Shore D. In analternative embodiment, the inner cover layer is comprised of apartially or fully neutralized ionomer, a thermoplastic polyesterelastomer such as Hytrel™, commercially available form DuPont, athermoplastic polyether block amide, such as Pebax™, commerciallyavailable from Arkema, Inc., or a thermoplastic or thermosettingpolyurethane or polyurea, and the outer cover layer is comprised of anionomeric material. In this alternative embodiment, the inner coverlayer has a hardness of less than about 60 Shore D and the outer coverlayer has a hardness of greater than about 55 Shore D and the innercover layer hardness is less than the outer cover layer hardness.

As discussed above, the core structure of this invention may be enclosedwith one or more cover layers. In one embodiment, a multi-layered covercomprising inner and outer cover layers is formed, where the inner coverlayer has a thickness of about 0.01 inches to about 0.06 inches, morepreferably about 0.015 inches to about 0.040 inches, and most preferablyabout 0.02 inches to about 0.035 inches. In this version, the innercover layer is formed from a partially- or fully-neutralized ionomerhaving a Shore D hardness of greater than about 55, more preferablygreater than about 60, and most preferably greater than about 65. Theouter cover layer, in this embodiment, preferably has a thickness ofabout 0.015 inches to about 0.055 inches, more preferably about 0.02inches to about 0.04 inches, and most preferably about 0.025 inches toabout 0.035 inches, with a hardness of about Shore D 80 or less, morepreferably 70 or less, and most preferably about 60 or less. The innercover layer is harder than the outer cover layer in this version. Apreferred outer cover layer is a castable or reaction injection moldedpolyurethane, polyurea or copolymer, blend, or hybrid thereof having aShore D hardness of about 40 to about 50. In another multi-layer cover,dual-core embodiment, the outer cover and inner cover layer materialsand thickness are the same but, the hardness range is reversed, that is,the outer cover layer is harder than the inner cover layer. For thisharder outer cover/softer inner cover embodiment, the ionomer resinsdescribed above would preferably be used as outer cover material.

Golf Ball Construction

As described above, the inner core preferably is formed by a castingmethod. The intermediate and outer core layers, which surround the innercore, are formed by molding compositions over the inner core.Compression or injection molding techniques may be used to form theother layers of the core sub-assembly. Then, the casing and/or coverlayers are applied over the core sub-assembly. Prior to this step, thecore structure may be surface-treated to increase the adhesion betweenits outer surface and the next layer that will be applied over the core.Such surface-treatment may include mechanically or chemically-abradingthe outer surface of the core. For example, the core may be subjected tocorona-discharge, plasma-treatment, silane-dipping, or other treatmentmethods known to those in the art.

The cover layers are formed over the core or ball sub-assembly (the corestructure and any casing layers disposed about the core) using asuitable technique such as, for example, compression-molding,flip-molding, injection-molding, retractable pin injection-molding,reaction injection-molding (RIM), liquid injection-molding, casting,spraying, powder-coating, vacuum-forming, flow-coating, dipping,spin-coating, and the like. Preferably, each cover layer is separatelyformed over the ball subassembly. For example, an ethylene acidcopolymer ionomer composition may be injection-molded to producehalf-shells. Alternatively, the ionomer composition can be placed into acompression mold and molded under sufficient pressure, temperature, andtime to produce the hemispherical shells. The smooth-surfacedhemispherical shells are then placed around the core sub-assembly in acompression mold. Under sufficient heating and pressure, the shells fusetogether to form an inner cover layer that surrounds the sub-assembly.In another method, the ionomer composition is injection-molded directlyonto the core sub-assembly using retractable pin injection molding. Anouter cover layer comprising a polyurethane or polyurea composition overthe ball sub-assembly may be formed by using a casting process.

After the golf balls have been removed from the mold, they may besubjected to finishing steps such as flash-trimming, surface-treatment,marking, coating, and the like using techniques known in the art. Forexample, in traditional white-colored golf balls, the white-pigmentedcover may be surface-treated using a suitable method such as, forexample, corona, plasma, or ultraviolet (UV) light-treatment. Then,indicia such as trademarks, symbols, logos, letters, and the like may beprinted on the ball's cover using pad-printing, ink-jet printing,dye-sublimation, or other suitable printing methods. Clear surfacecoatings (for example, primer and top-coats), which may contain afluorescent whitening agent, are applied to the cover. The resultinggolf ball has a glossy and durable surface finish.

In another finishing process, the golf balls are painted with one ormore paint coatings. For example, white primer paint may be appliedfirst to the surface of the ball and then a white top-coat of paint maybe applied over the primer. Of course, the golf ball may be painted withother colors, for example, red, blue, orange, and yellow. As notedabove, markings such as trademarks and logos may be applied to thepainted cover of the golf ball. Finally, a clear surface coating may beapplied to the cover to provide a shiny appearance and protect any logosand other markings printed on the ball.

In FIG. 4, a cross-sectional view of one version of a golf ball that canbe made in accordance with this invention is generally indicated at(21). The ball (21) contains a multi-layered core having an inner core(24), intermediate core layer (26), and outer core layer (28) surroundedby a single-layered cover (30).

In another version, as shown in FIG. 5, the golf ball (31) contains amulti-layered core (32) having an inner core (32 a), intermediate corelayer (32 b), and outer core layer (32 c). The multi-layered core (32)is surrounded by a multi-layered cover (34) having an inner cover layer(34 a) and outer cover layer (34 b). Lastly, in FIG. 6, a six-piece ball(35) containing a multi-layered core (36) comprising inner (36 a),intermediate (36 b), and outer core (36 c) layers is shown. A casing ormantle layer (38) is disposed between the core structure (36) andmulti-layered cover (40). The ball may include one or more casing layers(38). The multi-layered cover (40) includes inner (40 a) and outer (40b) cover layers.

Different ball constructions can be made using the core construction ofthis invention as shown in FIGS. 1-6 discussed above. Such golf ballconstructions include, for example, four-piece, five-piece, andsix-piece constructions. It should be understood that the golf ballsshown in FIGS. 1-6 are for illustrative purposes only, and they are notmeant to be restrictive. Other golf ball constructions can be made inaccordance with this invention.

For example, other constructions include a core sub-assembly having afoam or non-foam inner core (center); a foam or non-foam intermediatecore layer; and a foam or non-foam outer core layer. Dual-coresub-assemblies (inner core and outer core layer), wherein the inner coreand/or the outer core layer is foamed also may be made. Furthermore, theinner cover layer, which surrounds the core sub-assembly, may be foamedor non-foamed. As discussed above, thermoplastic and thermoset foamcompositions may be used to form the different layers. Where more thanone foam layer is used in a single golf ball, the foamed composition maybe the same or different, and the composition may have the same ordifferent hardness or specific gravity values. For example, a golf ballmay contain a dual-core having a foamed center with a specific gravityof about 0.40 g/cc and a geometric center hardness of about 50 Shore Cand a center surface hardness of about 75 Shore C that is formed from apolyurethane composition and an outer core layer that is formed from afoamed highly neutralized ionomer composition, wherein the outer corelayer has a specific gravity of about 0.80 g/cc and a surface hardnessof about 80 Shore C.

Test Methods

Hardness.

The center hardness of a core is obtained according to the followingprocedure. The core is gently pressed into a hemispherical holder havingan internal diameter approximately slightly smaller than the diameter ofthe core, such that the core is held in place in the hemisphericalportion of the holder while concurrently leaving the geometric centralplane of the core exposed. The core is secured in the holder byfriction, such that it will not move during the cutting and grindingsteps, but the friction is not so excessive that distortion of thenatural shape of the core would result. The core is secured such thatthe parting line of the core is roughly parallel to the top of theholder. The diameter of the core is measured 90 degrees to thisorientation prior to securing. A measurement is also made from thebottom of the holder to the top of the core to provide a reference pointfor future calculations. A rough cut is made slightly above the exposedgeometric center of the core using a band saw or other appropriatecutting tool, making sure that the core does not move in the holderduring this step. The remainder of the core, still in the holder, issecured to the base plate of a surface grinding machine. The exposed‘rough’ surface is ground to a smooth, flat surface, revealing thegeometric center of the core, which can be verified by measuring theheight from the bottom of the holder to the exposed surface of the core,making sure that exactly half of the original height of the core, asmeasured above, has been removed to within 0.004 inches. Leaving thecore in the holder, the center of the core is found with a center squareand carefully marked and the hardness is measured at the center markaccording to ASTM D-2240. Additional hardness measurements at anydistance from the center of the core can then be made by drawing a lineradially outward from the center mark, and measuring the hardness at anygiven distance along the line, typically in 2 mm increments from thecenter. The hardness at a particular distance from the center should bemeasured along at least two, preferably four, radial arms located 180°apart, or 90° apart, respectively, and then averaged. All hardnessmeasurements performed on a plane passing through the geometric centerare performed while the core is still in the holder and without havingdisturbed its orientation, such that the test surface is constantlyparallel to the bottom of the holder, and thus also parallel to theproperly aligned foot of the durometer.

The outer surface hardness of a golf ball layer is measured on theactual outer surface of the layer and is obtained from the average of anumber of measurements taken from opposing hemispheres, taking care toavoid making measurements on the parting line of the core or on surfacedefects, such as holes or protrusions. Hardness measurements are madepursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plastic byMeans of a Durometer.” Because of the curved surface, care must be takento ensure that the golf ball or golf ball sub-assembly is centered underthe durometer indenter before a surface hardness reading is obtained. Acalibrated, digital durometer, capable of reading to 0.1 hardness unitsis used for the hardness measurements. The digital durometer must beattached to, and its foot made parallel to, the base of an automaticstand. The weight on the durometer and attack rate conforms to ASTMD-2240.

In certain embodiments, a point or plurality of points measured alongthe “positive” or “negative” gradients may be above or below a line fitthrough the gradient and its outermost and innermost hardness values. Inan alternative preferred embodiment, the hardest point along aparticular steep “positive” or “negative” gradient may be higher thanthe value at the innermost portion of the inner core (the geometriccenter) or outer core layer (the inner surface)—as long as the outermostpoint (i.e., the outer surface of the inner core) is greater than (for“positive”) or lower than (for “negative”) the innermost point (i.e.,the geometric center of the inner core or the inner surface of the outercore layer), such that the “positive” and “negative” gradients remainintact.

As discussed above, the direction of the hardness gradient of a golfball layer is defined by the difference in hardness measurements takenat the outer and inner surfaces of a particular layer. The centerhardness of an inner core and hardness of the outer surface of an innercore in a single-core ball or outer core layer are readily determinedaccording to the test procedures provided above. The outer surface ofthe inner core layer (or other optional intermediate core layers) in adual-core ball are also readily determined according to the proceduresgiven herein for measuring the outer surface hardness of a golf balllayer, if the measurement is made prior to surrounding the layer with anadditional core layer. Once an additional core layer surrounds a layerof interest, the hardness of the inner and outer surfaces of any inneror intermediate layers can be difficult to determine. Therefore, forpurposes of the present invention, when the hardness of the inner orouter surface of a core layer is needed after the inner layer has beensurrounded with another core layer, the test procedure described abovefor measuring a point located 1 mm from an interface is used.

Also, it should be understood that there is a fundamental differencebetween “material hardness” and “hardness as measured directly on a golfball.” For purposes of the present invention, material hardness ismeasured according to ASTM D2240 and generally involves measuring thehardness of a flat “slab” or “button” formed of the material. Surfacehardness as measured directly on a golf ball (or other sphericalsurface) typically results in a different hardness value. The differencein “surface hardness” and “material hardness” values is due to severalfactors including, but not limited to, ball construction (that is, coretype, number of cores and/or cover layers, and the like); ball (orsphere) diameter; and the material composition of adjacent layers. Italso should be understood that the two measurement techniques are notlinearly related and, therefore, one hardness value cannot easily becorrelated to the other. Shore hardness (for example, Shore C or Shore Dhardness) was measured according to the test method ASTM D-2240.

Compression.

As disclosed in Jeff Dalton's Compression by Any Other Name, Science andGolf IV, Proceedings of the World Scientific Congress of Golf (EricThain ed., Routledge, 2002) (“J. Dalton”), several different methods canbe used to measure compression, including Atti compression, Riehlecompression, load/deflection measurements at a variety of fixed loadsand offsets, and effective modulus. For purposes of the presentinvention, compression refers to Soft Center Deflection Index (“SCDI”).The SCDI is a program change for the Dynamic Compression Machine (“DCM”)that allows determination of the pounds required to deflect a core 10%of its diameter. The DCM is an apparatus that applies a load to a coreor ball and measures the number of inches the core or ball is deflectedat measured loads. A crude load/deflection curve is generated that isfit to the Atti compression scale that results in a number beinggenerated that represents an Atti compression. The DCM does this via aload cell attached to the bottom of a hydraulic cylinder that istriggered pneumatically at a fixed rate (typically about 1.0 ft/s)towards a stationary core. Attached to the cylinder is an LVDT thatmeasures the distance the cylinder travels during the testing timeframe.A software-based logarithmic algorithm ensures that measurements are nottaken until at least five successive increases in load are detectedduring the initial phase of the test. The SCDI is a slight variation ofthis set up. The hardware is the same, but the software and output haschanged. With the SCDI, the interest is in the pounds of force requiredto deflect a core x amount of inches. That amount of deflection is 10%percent of the core diameter. The DCM is triggered, the cylinderdeflects the core by 10% of its diameter, and the DCM reports back thepounds of force required (as measured from the attached load cell) todeflect the core by that amount. The value displayed is a single numberin units of pounds.

Drop Rebound.

By “drop rebound,” it is meant the number of inches a sphere willrebound when dropped from a height of 72 inches in this case, measuringfrom the bottom of the sphere. A scale, in inches is mounted directlybehind the path of the dropped sphere and the sphere is dropped onto aheavy, hard base such as a slab of marble or granite (typically about 1ft wide by 1 ft high by 1 ft deep). The test is carried out at about72-75° F. and about 50% RH

Coefficient of Restitution (“COR”).

The COR is determined according to a known procedure, wherein a golfball or golf ball sub-assembly (for example, a golf ball core) is firedfrom an air cannon at two given velocities and a velocity of 125 ft/s isused for the calculations. Ballistic light screens are located betweenthe air cannon and steel plate at a fixed distance to measure ballvelocity. As the ball travels toward the steel plate, it activates eachlight screen and the ball's time period at each light screen ismeasured. This provides an incoming transit time period which isinversely proportional to the ball's incoming velocity. The ball makesimpact with the steel plate and rebounds so it passes again through thelight screens. As the rebounding ball activates each light screen, theball's time period at each screen is measured. This provides an outgoingtransit time period which is inversely proportional to the ball'soutgoing velocity. The COR is then calculated as the ratio of the ball'soutgoing transit time period to the ball's incoming transit time period(COR=V_(out)/V_(in)=T_(in)/T_(out)).

The present invention is illustrated further by the following Examples,but these Examples should not be construed as limiting the scope of theinvention.

Examples

In the following Examples, different foam formulations were used toprepare core samples using the above-described molding methods. Thedifferent formulations are described in Tables 3 and 4 below.

TABLE 3 (Sample A) Ingredient Weight Percent 4,4 Methylene DiphenylDiisocyanate (MDI) 14.65% Polyetratmethylene ether glycol (PTMEG 2000)34.92% *Mondur ™ 582 (2.5 fn) 29.11% Trifunctional caprolactone polyol(CAPA 3031) (3.0 fn) 20.22% Water 0.67% **Niax ™ L-1500 surfactant 0.04%*** KKAT ™ XK 614 catalyst 0.40% Dibutyl tin dilaurate (T-12) 0.03%*Mondur ™ 582 (2.5 fn)—polymeric methylene diphenyl diisocyanate (p-MDI)with 2.5 functionality, available from Bayer Material Science. **Niax ™L-1500 silicone-based surfactant, available from Momentive SpecialtyChemicals, Inc. *** KKAT ™ XK 614 zinc-based catalyst, available fromKing Industries.The resulting spherical core Sample A (0.75 inch diameter) had a densityof 0.45 g/cm³, a compression (SCDI) of 75, and drop rebound of 46% basedon average measurements using the test methods as described above.

TABLE 4 (Sample B) Ingredient Weight Percent Mondur ™ 582 (2.5 fn)30.35% *Desmodur ™ 3900 aliphatic 30.35% **Polymeg ™ 650 19.43%***Ethacure ™ 300 19.43% Water 0.31% Niax ™ L-1500 surfactant 0.04%Dibutyl tin dilaurate (T-12) 0.09% *Desmodur ™ 3900—polyfunctionalaliphatic polyisocyanate resin based on hexamethylene diisocyanate(HDI), available from Bayer Material Science. **Polymeg ™650—polyetratmethylene ether glycol, available from Lyondell ChemicalCompany. ***Ethacure ™ 300—aromatic diamine curing agent, available fromAlbemarle Corp.The resulting spherical core Sample B (0.75 inch diameter) had a densityof 0.61 g/cm³, a compression (SCDI) of 160, and drop rebound of 56%based on average measurements using the test methods as described above.

When numerical lower limits and numerical upper limits are set forthherein, it is contemplated that any combination of these values may beused. Other than in the operating examples, or unless otherwiseexpressly specified, all of the numerical ranges, amounts, values andpercentages such as those for amounts of materials and others in thespecification may be read as if prefaced by the word “about” even thoughthe term “about” may not expressly appear with the value, amount orrange. Accordingly, unless indicated to the contrary, the numericalparameters set forth in the specification and attached claims areapproximations that may vary depending upon the desired propertiessought to be obtained by the present invention.

All patents, publications, test procedures, and other references citedherein, including priority documents, are fully incorporated byreference to the extent such disclosure is not inconsistent with thisinvention and for all jurisdictions in which such incorporation ispermitted.

It is understood that the compositions and golf ball products describedand illustrated herein represent only some embodiments of the invention.It is appreciated by those skilled in the art that various changes andadditions can be made to compositions and products without departingfrom the spirit and scope of this invention. It is intended that allsuch embodiments be covered by the appended claims.

We claim:
 1. A core assembly for a golf ball, comprising: i) an innercore layer comprising a foamed composition, the inner core layer havinga diameter in the range of about 0.100 to about 1.100 inches, a specificgravity (SG_(inner)), and an outer surface hardness(H_(inner core surface)) and a center hardness (H_(inner core center)),the H_(inner core surface) being greater than the H_(inner core center)to provide a positive hardness gradient; ii) an intermediate core layercomprising a thermoplastic material, the intermediate layer beingdisposed about the inner core and having a thickness in the range ofabout 0.050 to about 0.400 inches, a specific gravity(SG_(intermediate)), and an outer surface hardness(H_(outer surface of IC)) and an inner surface hardness(H_(inner surface of IC)), the H_(outer surface of IC) being greaterthan the H_(inner surface of IC) to provide a positive hardnessgradient; and iii) an outer core layer comprising a thermoset material,the outer core layer being disposed about the intermediate core layerand having a thickness in the range of about 0.200 to about 0.750inches, a specific gravity (SG_(outer)), and an outer surface hardness(H_(outer surface of OC)) and an inner surface hardness(H_(inner surface of OC)), the H_(outer surface of OC) being the same orless than the H_(inner surface of OC) to provide a zero or negativehardness gradient, wherein the SG_(outer) is greater than theSG_(inner), and the SG_(intermediate) is greater than the SG_(inner). 2.The core assembly of claim 1, wherein the inner core comprises a foamedpolyurethane composition.
 3. The core assembly of claim 1, wherein thethermoplastic material of the intermediate core is an ethylene acidcopolymer containing acid groups such that 70% or less of the acidgroups are neutralized.
 4. The core assembly of claim 1, wherein thethermoplastic material of the intermediate core is an ethylene acidcopolymer containing acid groups such that greater than 70% of the addgroups are neutralized.
 5. The core assembly of claim 1, wherein thethermoset material of the outer core is a polybutadiene rubber.
 6. Acore assembly for a golf ball, comprising: i) an inner core layercomprising a foamed composition, the inner core layer having a diameterin the range of about 0.100 to about 1.100 inches, a specific gravity(SG_(inner)), and an outer surface hardness (H_(inner core surface)) anda center hardness (H_(inner core center)), the H_(inner core surface)being greater than the H_(inner core center) to provide a positivehardness gradient; ii) an intermediate core layer comprising athermoplastic material, the intermediate layer being disposed about theinner core and having a thickness in the range of about 0.050 to about0.400 inches, a specific gravity (SG_(intermediate)), and an outersurface hardness (H_(outer surface of IC)) and an inner surface hardness(H_(inner surface of IC)) the H_(outer surface of IC) being greater thanthe H_(inner surface of IC) to provide a positive hardness gradient; andiii) an outer core layer comprising a thermoset material, the outer corelayer being disposed about the intermediate core layer and having athickness in the range of about 0.200 to about 0.750 inches, a specificgravity (SG_(outer)), and an outer surface hardness(H_(outer surface of OC)) and an inner surface hardness(H_(inner surface of OC)) the H_(outer surface of OC) being greater thanthe H_(inner surface of OC) to provide a positive hardness gradient,wherein the SG_(outer), is greater than the SG_(inner), and theSG_(intermediate) is greater than the SG_(inner).
 7. The core assemblyof claim 6, wherein the inner core comprises a foamed polyurethanecomposition.
 8. The core assembly of claim 6, wherein the thermoplasticmaterial of the intermediate core is an ethylene acid copolymercontaining acid groups such that 70% or less of the acid groups areneutralized.
 9. The core assembly of claim 6, wherein the thermoplasticmaterial of the intermediate core layer is an ethylene acid copolymercontaining acid groups such that, greater than 70% of the acid groupsare neutralized.
 10. The core assembly of claim wherein the thermosetmaterial of the outer core is a polybutadiene rubber.